Find someone selling their H/C/I set-up, add long tubes, ory, and a good clutch and shifter, and some drag radials and sub frame connectors or LCA's to boot. I bet if you shop used you can get at least a cam, intake, headers, ory, clutch, shifter, dr's, sfc's and lca's for 3500. Granted you will have to do the install yourself, but that's the whole point in owning a car like this to get familiar with it so when something happens you know exactly what to do and how to do it.
You may even be able to score a set of 243 heads, LS6 intake, FTRA, Headers, ORY, clutch, DR's, and LCA's for 3500 for sure 4500. Hell for 4500 you could score a fast intake, but I'd skip the fast for a LS6 and use that money for injectors and fuel system so you will be ready to spray the **** out of it when you want to