What transmission can I use
 

Im on a budget for my 69 camaro which has 475hp at the crank. The aftermarket transmissions I have found such as monster transmission and tremec are above my budget. I was wondering if i could retrofit a transmission from a different make and model. I.e the 2010 jaguar XKR makes 510hp, so could i find one of those from the salvage yard and put it on my 383.

i guess you are stuck lookin for a good used hp trans. for a quality built 700 r4 that handles up to 500hp your lookin at 2k for the trans and probly around 3 hundred for the adapting. couple hundred for misc.

Sorry man, but "475 hp" and "economy drivetrain" just don't go together. To get a Jaguar trans to work would require having an adapter between it and the engine. I doubt anything like that exists in the aftermarket, because frankly you'd probably one of the only ones who would want to do that. Keep your eyes open for a good used trans, I've seen some for sale from time to time. What trans do you have now, and how about the rearend too? With that engine, you need to beef up everything; trans, driveshaft, u-joints, and rearend. If any of those are left as they came stock, it will be the weak link and the first thing to break.

could i find a salvaged trans that does work with my car and beef that up? new gears, sun shield, planetary gears, etc

rebuilding a auto trans is not a easy project. requires some specialty tools. heres a couple sites with some info.
Performance Transmissions and Parts from PATC 700R4 AOD 4L80E 48RE
700R4 & 4L60E Automatic transmissions specialists - ProBuilt