I think the last year for the 502 was 2002.
There are no decent "bolt-ons" for the 502 if you want to keep the EFI.
The kit Kamma spoke of from Tyler is a great kit but it's about $6k per engine. I have heard nothing but good things about Vortech superchargers for the 502 but again about $6k. It would be nice if there was something out there that was "in-between" for a couple thousand that would get you 40-50 TRUE hp!