The current paxton supercharger for carbureted engines runs around 2800 bucks for the satin version and a bit more for the polished version. it is designed for a stock 289. that does not mean that what the others say about building up the bottom end and especially the head-gaskets are not a good idea.
(ask me how I know


) it is a very easy to install kit, well designed and I have had it on my car for about 5 years now with no problems except a blown head gasket. good luck.
btw you will get between 30 to 70 percent increase in power the more efficient your engine is to begin with the more it will get out of it. this kit only makes about 6 psi of boost in as packaged form so it can be placed on a stock engine without doing to much too it. If you do end up rebuilding the car a lower compression ratio and forged pistons would be a good idea.
here is a link to their website.
http://www.paxtonauto.com/systems_1001839.html