Best way I've heard to get any real HP increases out of these motors is to deck it to raise the compression ratio. Stock compression is pretty pathetic.
I've heard that BB Chevy valves will work in that engine with some slight mods. Not sure if that's true or not, so don't hold me to it. Might be worth looking into, though.
I know that the older Roadmasters had a factory compound dual carb manifold/exhaust set up. I've seen them on ebay go for anywhere around $200-$400 bucks. I'm not sure what exactly you would accomplish as far as CFM ratings were concerned. Those older compound set ups stack up two 2 barrel Strombergs, while the newer guys have the stock single Stromberg or Carter 4 barrels. I don't think you would gain much horsepower with the dual setup, but it would sure look cool as hell.
Also, I know that Edmunds made a dual intake manifold for the 320s. I'm not sure what the rules are on this message board about posting other web site addresses, so if you're interested, shoot me an email and I'll tell you where you can get them.
If you want a cruiser, keep the stock tranny in it. If you're looking for performance you're going to need to swap it out....right now before you do anything else. Expect to shell out the dough, though. All the adapters I've seen go for well over $500. Then you have to think about the driveshaft and rearend swap. It's quite the task. I've heard of some guys that have modified the bell housings on some Muncie trannys to bolt up to the 320s and have been able to keep the stock enclosed driveshaft and rearend. Other than cost, I don't see why you would want to do that over the later.
Good luck. Keep us posted.
