There’s a series of books from Railhead Publications called “Critters.” There are 4 volumes, and they feature manufacturer ads and specs for a variety of industrial diesels. Most of these are 2-axle types in a variety of flavors.
If you can find an older LGB 2090 diesel, that might be a good place to start. I did a very simple conversion of one when I was a teenager that has since been de-motored and is now used by my son to push around the railroad.
I’ll be working on upscaling a 1:29 NW-2 to 1:22 for my dad’s railroad this spring. (I’m waiting for the new G-wire receivers to show up before having everything shipped out to me.) I just finished installing a Revolution in a friend’s NW-2, and took the liberty while it was here to make notes of what I’d do to it–most of it along similar lines to what Ray did with his RS-3 conversion; larger cab, adding a bit of width to it, and new front/rear pilots.
Andrew already posted links to my “downsized” B’mann 45-tonner, but if you’ve got the trucks, that’s not a bad place to start, either. A simple boxcab a la Bruce Chandler (either his 4-axle or 2-axle job) wouldn’t take a ton of time to scratchbuild.
Later,
K