Well... next thing to do is drop a 350 in it.. I have two at the shop right now that have 350's in them.. Man they are quick with the right rear gearing.
You are going to find that there is only so many things you can do to a 4.3 besides turbos and nitro that doesn't require a big step up. The project I'm working on now is an 88' C30 1ton Dually with a punched out 454 big block for a company that hauls race trailers.. They weren't happy with the old and tired 454 so they brought it to me to make it bigger and better. I have a machine shop close that I work with and also an engine dyno shop that can tell me what the numbers are before dropping the engine in... I've done a few 4.3's.. my friend's included.. But his is a true sleeper and his only problem is that he can't hook up because of his gearing.
Dom
