Just for reference, I have 3.38 gears with a 3 speed OD trans (1968 1st gear synchro Saginaw) in my 1957 Chevy NAPCO truck. It works just fine for me. However, I do have a warmed over 283. I was concerned with the same issues as mentioned in this thread relative to bogging down. But the 283 seems to help mitigate that issue. I got my gears from Patrick's. He gave a discount because I bought two sets (front and rear) and was most helpful.
Note:
I had 3.90 gears, but the front differential had some chipped teeth, so I had to replace them anyway and opted for the 3.38s. I'm working on rebuilding a 348 engine, so if long-term the 283 doesn't cut it, I'll go with the bigger engine (I need something to keep busy).
don
