Ya, i mean a whole new/used longblock, the results are awesome. You did say you like taking off fast and not speeding, so the 4.8L should be just fine. 4.56 gears!!!!!!!!! !!! holy cow, lol, that will def. get you some take off, plus the posi, seee yyaaaaaa!!!

If you go over .500 or somewhere around there, you'll have to upgrade to new springs. Is that what you were asking?

As far as the cam, get something that is going to suite your driving habits, if you like to take off fast and race light to light, get a cam that is in that rpm range, something that starts around 1500rpms.
Headers are a good addition to any cam.
For more info, or a collection of cams that domeskilla put together, check here: http://www.ls1truck.com/reference/camspecs.html

Those 4.56 gears are going to pretty steep, my 4.10's are great, but i don't see ever going lower than that. What size tire do you have, the circumference? That will make a difference too.

Sounds like you're on the right track then, if you want some spunkyness to that 4.8L, a cam/headers/4.56/posi are the way to go. Maybe a underdrive pulley, and if you don't already have them, LS1 fans.

good luck,

allen