Ryan, haha. Project creep starting to set in I see. Nice engine. Great power delivery for its size. I’ve looked on CL in the boating section from time to time, for a used 15 or 20 hp universal diesel. Same footprint as the old atomic 4, but of course, diesel, and a fine running, low speed engine. I think these were 1800 RPm models, if I remember correctly. Not so ear splitting as modern day high speed bangers at top RPM. They show up once in awhile, couple of times a year. But Iam not diligent enuf to wait in the lair until one passes by.
I can pull my old yard goat into the shop and take a closer look at the undercarriage - see exactly what I could do there for trucks. Maybe mid week next.
One immediate question - what are your general dimensions for your existing drawings. Height and length of sideframes mainly. Actually the overall length is the key. I could interpolate how big the trucks might need to be with this info.
BTW, the Whitcomb 60 ton loco on the Hawaiian Railway (36”NG) has an interesting drive chain - the wheels on each truck are connected via a main rod. So one set of drivers powers the other driver on the same truck, similar to steam loco main rods.
Also Here is a photo of the trucks for a Whitcomb 45 ton diesel electric, similar if not identical to your drawing. The wheel sets and bearings move up and down in the frame in a manner similar to what you designed and made up for the passenger car trucks we bought late last year.
Glenn