The most cost effective purchase you can make for your race car would be a new light weight body. For far less than the price of a race engine you get one of several new light-weight bodies. Total weight + - 100 lbs. Imagine how much better your acceleration will be, and how much less wear and tear you will have on your driveline.
 When building a race vehicle you obviously want it as light as possible. So you cut out the floor pan - wheel wells & inner structure..... So as far as the body all you are left with is an overweight, floppy shell, held together with old factory spot welds and body lead.  Our race weight bodies are manufactured from extremely complex molds - which produce a rigid one piece unit. The roof, quarters & firewall are generally stiffened with the use of internal ribbing. Light weight race weight bodies have NO floor or interior panels, windows come blanked in.  These race weight bodies are designed for competition use only. Fiberglass bodies can be made heavier or lighter (within reason) depending on your application. Average body weight is anywhere from 75# to 100# depending on make and model. 
 Installation is a snap!  Whether you are installing just the body or an entire package, the bodies attach at the rocker panels, tail pan, trunk jam, door jam, and front and rear window jams.