I've seen those buses at a station somewhere, maybe Whitefish Montana or near there. What I really need to know is the manufacturer(s) , in the case of buses it is often 2, you may have a GMC chassis and some other company builds the body. In order to do a 3D model I need either a good set of drawings (top, bottom, left, right, front & back) OR an HO scale model I can buy to copy the dimensions. One good candidate is the Ford Transit Bus which was in production from 1936 to 47: https://en.wikipedia.org/wiki/Ford_Transit_Bus
The Ford's a good choice for urban transit. They were as common as anything before the New Look. Try plugging 'Ford Crackerbox' in your search engine while researching it. For intercity, you may find a great deal of both information on, and interest in, the Flxible Clipper. Note the spelling; it's correct. You'll find the Flxible easier if you've already programmed 'fluted' (corrugated) metal bodysides.
Very nice! Flxible partnered with Twin Coach in those days for urban transit bus production. Twin Coach made some nice, handsome coaches, and they were as common as Ford Crackerboxes. Unfortunately, they were different enough from Clippers, Visicoaches and Starliners that you'd almost be starting from scratch.
The nickname is a "bruck" ("bus" and "truck" combined). No diagram yet, but here's a history: http://www.oil-electric.com/2009/05/innovation-bruck.html MKS
The chassis for the 1928 Ford BB series truck, short wheelbase in N scale. This is the first test print, lots of things still to add. You can see the legendary "flathead" V8 beginning to take shape.
The 'legendary flathead V-8' was not yet a gleam in Henry's eye in 1928. I think you're after 1932, or (judging from the prototype pic above) 1933. I also think you're after something like the Model 46, considering the BB had four cylinders.
The Rapido New Look bus will be out soon in HO Scale. See http://rapidotrains.com/ho-new-look-bus/. The links are worth looking at, as is the rest of the site. Jason is a madman, but, fortunately for the human race, channels his madness into good and fun things.
That looks amazing, however I just received one of these kits in the mail last week so I'll be doing this one first: Built By Mike Habersack http://www.1-87vehicles.org/photo515/ford_transit_bus.php
That looks interesting, too. Jason bought a real New Look bus, as you may have seen on the Rapido site. It's almost as detailed as his model. I've seen both his actual bus and the test shots of the model.