Not much. It'll take a 600 ok. You'll need to upgrade the exhaust "somehow". Either add headers or bore out the exhaust manifold like I had my friend Freddie do for me. You can read about it here:
Exhaust Manifold Mod
It's not hard to do, but I chose to let Freddie do it because my skills with a hand held grinder suck. I never would have thought there would have been that much meat in the outlet of a slant exhaust manifold but there is.
Also, a nice high flow air cleaner won't hurt. While internal engine mods are not necessary, it won't hurt to have the head milled, re-cam it if you want to go that far. It just depends on how far you want to go. As long as you use a vacuum secondary 600, it'll be fine as you can adjust the secondaries with the diaphragm springs.
