I'd have the numberboard/louver part of this done in an evening if I didn't have to wait for the glue to dry. Don't know what's so difficult about this...and here is how I'd do it in 24 easy steps:
(Givens: You've measured the dimensions of the stock numberboards and recorded them)
Tools and supplies: Tenax, fine spotting brush, 320 and 600 grit wet/dry sandpaper, 1" wide sticky masking tape, 1X3X6 piece of wood (smooth, flat sides), double sided mounting tape, sharp new #11 blades & knife handle to hold 'em, 6" steel rule (or straight edge), 6" caliper, fine small jeweler's files (at least "pointy-round" and "pointy-flat"), dental pick, assortment of drill bits, pin vice, assortment of sheet Styrene
Note: If you don't have a precision caliper, either go to Harbor Freight Tools and buy one for around 12 bucks, or do step 5 and 6 before step 1, using the existing numberboard on the side of the engine body as a pattern.
STEPS:
(1) Cut out old numberboard and louvers carefully w SHARP, NEW #11 BLADE, working slowly on both sides, making sure to save the louvers still mounted on the base material you cut out. It appears that the stock numberboard's top edge may be damaged by this excision. Don't worry about it. Set aside the removed louvers for later.
(2) File resultant hole to a sharp, rectangular shape keeping edges parallel and straight. You'll probably have to file off a bit of the remaining top edge of the stock numberboard...maybe...so do that too.
(3) Fill finished hole w a Styrene plug (should be only a few mils less than the engine body side) cut to as close a fit as you can, and glue in place using Tenax sparingly applied from the inside making sure the outside surface of the plug is even with the engine body surface. Let dry for at least a few hours.
(4) Fill and sand until plug's seams are invisible.
(5) Using .005" Styrene, cut out two rectangular shapes that match the dimensions and end radii of the stock numberboards you've removed and sand the edges so they're smooth, having no burrs and are perpendicular to face of the new numberboard shapes.
(6) Double check the shape of the numberboard shapes and make any adjustments NOW.
(7) Appropriately locate the new numberboard shapes on the sides of the engine body and spot "weld" them into place with a tiny amount of Tenax applied with a tiny spotting brush - hold for 15 seconds after spot-"welding" with steady, light to moderate pressure using a sharp, pointed instrument such as a dental pick, or something that is "sharp" but not sharp enough to puncture the outside surface of the numberboard shape. You don't want the tiny numberboard shape to be attached to whatever you're holding it with so when you remove your holder, the just-glued numberboard shapes stays on the engine body, and isn't stuck to the pointy holder.
(8 ) Run a bit more Tenax carefully between numberboard shape's insides surface and the engine body. DO NOT PRESS TOO HARD - molten plastic will ooze out between body & numberboard shape if you're pressing too hard, and you do not want this.
(9) Set aside to dry for a couple of hours.
(10) Trim each pair (keep them in pairs) of your saved excised louvers semi-close to the raised cast louvers on three outside sides of each set of paired louvers making sure not to damage or deform the louvers. Hand-trim the thickness of the pieces also so they're only about .020" to .030" thick under the louvers. Remember, keep them in pairs.
(11) Sand off any plastic burrs from the edges of each pair of salvaged and trimmed louvers.
(12) Attach the salvaged louvers to a smooth, flat piece of wood (handpiece) you can comfortably hold in your hand by using double-sided tape, pressing the louver sides of the of the pieces to the double sticky tape which has been mounted previously to the smooth wood handpiece.
(13) Carefully and slowly sand down the backsides of the trimmed louver pieces until there is a miniscule thickness of plastic under the louvers and on either side of them. Do this by taping down a sheet of 320 grit wet/dry sandpaper on a flat surface (tape four sides) and stroking the mounted salvaged louvers on this sheet of sandpaper, checking after EVERY STROKE to make sure you're thinning the backsides evenly. This will go better if you use a bit of water to collect the plastic dust and increase the cutting qualities of the sandpaper.
(14) Carefully trim and dress the sides of the sanded and trimmed louver pieces so the newly thinned "base" doesn't protrude out from the sides, tops and bottoms of the louvers. The new base should be less than .003" thick...but you can make it even thinner...be careful...it should only be an RCH thick...almost translucent. You now have four individual sets of louvers that match the other louvers on the engine's body.
(15) Set your newly liberated louvers aside in a safe place, 'cause of you lose 'em, they'll be difficult to replace.
(16) Drill clearance holes into your securely bonded and dry numberboard shapes which are now monolithically glued to the sides of your engine body. These clearance holes should be smaller than the width of the shaped hole you are about to create, but large enough to get the point of a small jeweler's pointy-round file into.
(17) Using small, fine jeweler's files, start filing the numberboard's inner contours by filing carefully and slowly. You want to create a very thin and even raised numberboard edge. It's easy to remove material, but much more difficult to add it if you take away too much. Try to keep the inside edges of the lozenge-shaped hole you're creating perpendicular to the outside surface of the engine body.
(18) After you're satisfied with the raised numberboard edge you've just created (if .005" is too tall, carefully sand the edges down using a small sanding block with 600 grit paper using very light and careful strokes until you're satisfied), cut plugs for these holes from Styrene that is several mils thinner than the wall thickness of the engine body. Match the shape of the hole closely because you want a "press-fit". Once again, work slowly. (If you wanted to illuminate your numberboards, you would make this plug from clear Styrene).
(19) Press the finished plugs into their matching holes, making sure they're slightly deeper than the surrounding engine body surface on the other side of the raised numberboard edge.
(20) Glue the properly positioned numberboard plugs in place using Tenax sparingly applied from the inside of the engine body.
(21) Locate your four set-aside liberated louvers and make sure they're oriented properly (finding "up" and "down")
(22) Now, position, hold and glue each set of louvers in place using the technique and cautions for gluing on the Styrene numberboard shapes you've previously done.
(23) Let dry for several hours
(24) You're DONE! ...at least with the numberboard/louver details...
Well, that wasn't too difficult, and I guarantee if you work carefully and double check everything, your results will be excellent.
Cheerio!
Bob Gilmore
