Bolt Ons

Can anyone tell me what the major differance is in the pre-1965 389ci? There's the problem, I have a '62 Catalina that's a cruiser. It has a bone stock 389. The only modification is I swapped out the generator for an altenator. All I want to do is upgrade the carb, intake manifold, and put in a set of headers, oh yeah, I also want to go electronic ignition. Everytime I question after market parts manufacturers, I get the same line, "we don't make anything for your application". I don't have a problem with carb replacement, I can always use a spacer to the stock manifold. So if there's anyone who can help, please! Keep in mind, it's a street cruiser, but a little giddyup could'nt hurt. Thanks