Originally posted by Steve VW:
Barth used Cummins engines in both the Breakaway models and some later Regencies. The Breakaways usually had 5.9 and the Regencies had 8.3.
The 8.3 Cummins was usually 300hp with some at 325. I have not seen stock engines of that vintage with 350 hp.
Both are straight sixes. As you suggested, they may not have the engine right. Most earlier Regencies had Gillig chassis and Cat 3208 engines of 250-300hp. Some were made with 8.3 Cummins but due to the short engine bay in the Gillig chassis the longer sixes would not fit. Those coaches had a Spartan chassis.
Should be easy to tell a straight six from a V8....
A 1989 would usually have a 4 speed Allison trans. 6 speed did not come out till later.
A good inspection would be valuable.