Keep it a 3.8 auto and enjoy it. Get it super clean inside and out. Fit some extractors and a K&N air filter and call it a day. Enjoy it. Stay with stock springs and 15" tyres and it'll fly under the cop radar, too.
If you still want more get some performance diff gears - about a 3.45 would be good while still streetable. You'll really feel the difference, lots more pickup off the line and in gear.
In the meantime you can keep a V8 aside and learn to properly build it. It might take years but when you're done you'll really appreciate it, and be legal as well.
- boingk