Not alot can be done with the V8 engine tbh. Remap, exhaust, piggie pipe and supercharger kit is about it tbh.
Remap will pop it up about 10-25hp but will sort out throttle control and smoothen power band to be a bit more eager low down. Exhaust frees things up as there are some serious exhaust blockages in the stock pipes (crimps, heavy exhaust packing, etc). Piggies will clean up the down pipes which releases a significiant (relative) amount of power. All done you should get nearing 400 or slightly over (engine health depending of course). Supercharger kit is a waste of time and money. Will give you about 450 for stupid money.
These engines dont have any space to play with them in the bay. The parts internally are not that strong so have minimal amount of ability to handle increased power.