Let me preface this by saying that I really like the 235. I'm building a '60 model now for my '54 Bel-Air.
The 235 is fairly simple to build and parts for the '55-'62 years are still plentiful. In our Pre-'55 Chevy vehicles, they are the only bolt-in option if you don't want to cut the frame.
1st answer: In this era, the GMC and Chevrolet engines are totally different design. Almost nothing will interchange, and internal construction is different.
The 235 has drawbacks in general, often not worth the work as a replacement for another make in the GM family. One is that most any buildable 235 core you find is going to require a complete rebuild. This will cost 1,000 in parts, easy. Head work alone can run 300-400 dollars for all new valves, springs, hardened seats, etc. My 235 with heavy performance mods will cost 4 grand total. And even then I'll only have 200 HP.
The head and main bolts are not available new. (Neither are GMC, but a 235 doesn't solve the problem) There are other bolts and pieces that require a donor motor if they are missing/damaged in the 235 to be built. I think the flywheels, clutches, motor mounts, engine size & weight are also different between GMC and Chevy.
The 235 has only 4 main bearings and a long stroke, so its RPM range is limited to short bursts of 4,000 RPM. Max cruising RPM is 3,200 RPM or so. It has no full-flow oil filter. 235s are also infamous for rear-main oil seal leaks. The 235 also had "tapered" main bearings, where each sucessive main journal is a larger outside diameter. #1 main is the smallest and #4 rear is the largest. It makes crank grinding and sizing more difficult for a shop thats used to post-'63 engines. Almost nobody can line-bore a 235 block because of this.
Stock 235s were good for 135 HP and 220 FT-Lbs of torque ('60 specs). I think the GMC motors made slightly more power stock.
Both the 228 GMC and 216-235-261 Chevy engine families are antique obsolete designs. If the owner wants a driver with a 6 cylinder, look into a more modern design. A '65-'74 250 or 292 are more modern design and will accept V8 style bellhousings and trannys.
Now having said that, will somebody remind me why we work on these 235s at all?
Good luck
chip
