BTW.. the 3 side rung car has 7 end ladder rungs, and the 4 side rung car has 8 end ladder rungs...
Ok... Now that I have time to sit down and look at A and B side photos of both versions of the car....
NAHX 550307 is a '3 Rung' car..
NAHX 550513 is a '4 Rung' car..
B End Left
B End Right
Here is what I can see
Stirrup Steps:
3 Rung has a single step.
4 Rung has 2 steps.
The Rungs:
3 Rungs has a grab iron on the sill (thicker sill), then 3 Rungs
4 Rung has no grab iron on the sill (thinner sill), then 4 Rungs.
Rung Placement:
On the 3 Rung, the first rung is at the top of the sill.
On the 4 Rung, the first Rung is roughly in the middle of the sill.
(by sill I mean flat vertical side before the curve of the hopper starts.)
End Ladders.
On Both cars, the side rungs are even with the end ladders.
However, due to the height and spacing of the rungs...
The 3 Rung Car has 7 ladder rungs above the sill with a grab iron at the sill.
The 4 Rung Car has 8 ladder rungs at/above the sill.
.. Although looking at the car overall, the ladder rung spacing seems to be roughly the same on both versions, the main difference is if the first rung is a rung or grab iron.
Roof walkway supports.
On B End Right / Pipe Side:
Both cars have similar spacing of supports Thick-Thin-Thick, Ect, with the 'short support' gap on the RIGHT side just left of the outlet pipe.
ON the A End Right / Non Pipe Side:
Both cars have similar spacing of supports Thick-Thin-Thick, Ect, with the 'short support' gap on the LEFT side.
With all that, I'd say.. you have a usable product that 9 of 10 modelers won't notice the issue.
But looking at your kit, it appears you have both the rung and grab iron when you should have 1 or the other.
If you did a Rev-2, you could do a 3 rung kit with a grab and and thicker end support. and a 4 rung kit with no grab and thinner end support.
Without knowing how the Walthers car is built exactly.. you could.
Flip the piping/floor 180 degrees and move the brake rigging to the opposite end.
or Flip the roof 180 degrees.
Assuming HO is the same as N.. they did get the roof bracket spacing correct on each side (only reversed 180 degrees from the brake rigging/pipping.)
That is what I can see that stands out with a bit of study.. I'm sure I'm missing things..
@Atlas Paul When you run your PD cars.. see if you can flip the roof insert 180 degrees..