It sounds as if you want a Type 'A' bus.
Generally speaking, if it has a 6.9L or 7.3L it has a pretty good engine. But most of those were hooked to an E4OD or 4R100 transmission. They were pretty bad when they were new and didn't last very long behind a diesel engine. There are some companies that specialize on building those transmissions into reliable transmissions that can handle the power, torque, shaking, and load put on them when they are in a bus or hopped up diesel 1-ton.
If it has the 6.0L, 6.4L, or 6.7L stay away from them as they are disasters waiting to happen that are hooked to the 4R100 transmission.
If it has the Ford 460 V-8 you can't afford to put gas in them. Where the diesels consistently got 11-14 MPG the 460 was lucky to get 6-9 MPG.
If it has the Ford V-10 the transmissions generally didn't have a lot of problems. The engines have some quirks but the different forums have a lot of people who know the work arounds to make those engines really perform. Fuel mileage will be in the 10-12 MPG range.
Most of the GM chassis buses under Type 'A' buses were G-3500 or G-4500 series. Regardless of engine, the transmissions were ALL a lot stouter and more reliable than the Ford transmissions.
The 6.2L diesel is a bit of slug but it is ultra reliable and just keeps plugging along. But at 140 HP it isn't going to get there very quickly. Fuel mileage will be in the 10-14 MPG range.
The 6.5L diesel in the G-series is an orphan that has virtually zero parts support for it. Most of the parts are common to the engines used in the C/K trucks and Suburbans and Hummers but there are a few application specific parts that are made out of unobtainium. And since they are wear parts you could find yourself dead in the water somewhere and no ability to get a replacement part you didn't make yourself.
GM used various gas engines in the G-series chassis. The most common was the 350/5.7L/Vortec 5700 V-8. The newer buses got the 6.0L engine. All of those engines work really well, live a long time, are easy to fix and find parts, and generally got 9-16 MPG depending on a lot of variables but you can pretty much count on 10-12 MPG with them. Very few G-series chassis got the 454/7.4L/Vortec 8100 just because most operators didn't want to spend the extra $$$ for them. And even fewer got the Duramax engine--$14,000.00 option that got 1 MPG better than the gas engine.
Some of the newer buses are showing up with the 5.3L V-8 and even some of them are showing up with the V-6--not bad but a little short on power for a bus.
I do not like the plastic body buses as conversion candidates. I know there are more than a couple of people on here who have done great conversions in plastic body buses. My problem with them is the marriage between the chassis and the plastic body is never that happy and they usually end in really ugly divorces characterized has major water leaks and crazing of the body panels.
The same can not be said about the yellow buses and the yellow buses that were painted white at the factory. The school buses are built to a different safety standard and generally hold up really well over time. I think because of the more rigid construction of the school bus body there is not as much flex in the body that causes most of the problems in the plastic buses.
Here are some you may want to consider:
Chevrolet 1995 Collins
GMC 1988 BLUEBIRD
Good luck and I hope you find the bus you want!
Linear Mode
