Miniatures by Eric makes louvered grills for SD40-2's
thank you, that's it, cool...
...I will glue them on a Kato SD40-2 non DB shell and modify the shell to fit the new drive, cab and sill (which is possible, I've done that already for the SOO #777 engine)
Another option would be to take the grills from an Atlas or Kato shell and sand the back down
so you can mount it like you would a casting...
unfortunately Kato shells are way too expensive to slaughter and the Atlas ones from a GP40 are too small, not long enough...