From 1939 to 1959 or 1962 the GMC family of engines...228,236,248,256,270,and 302 engines were all full pressure engines with precision bearings. The GMC castings also used a higher nickle content which will allow them to take higher rpm than a chevy. Maximum reccomended speed of the engine is 3400 rpm.
Performance parts for these Jimmy engines are available. They are on the pricey side. I am building a 302 for my 1940 GMC and expect to be in the 225- 250 hp range. These 6s are bulletproof engines and can take quite a bit of abuse and still get you home.
If you must go the bent 8 route, I suppose the 327/350 would be an excelent combination. Don't sell your 6 banger short. They are still highly sought after engines, and have a great sound, and smell!
In the end this is your truck, and you could do to it whatever you want. So Have fun with it. Whatever way you go, there are people here that have done it, are doing it, or will do it, and are ready to help.
Cheers
John
