Need help with aerodynamic basics

[Daren]

I'm doing a non-pro touring build on my 78 lincoln mkv. The car will be receiving a warmed over 460 punched up to 471, 100 shot of spray, has 3 speed auto, 2:47 gears and is in need serious aerodynamic help. Even with the original stock 460 engine at high speeds air pressures build up under the car and lifts the body upwards in an on and off motion followed by a strong up movement that scares you into letting off the throttle. It's scary and I probably shouldn't drive my car that fast I know. I'm not going to stop and I need some info about front air splitters, as in roughly what shape and where should I mount it (near front bumper or towards front tires, car has feet of front overhang), if at all? Would I be better off fabricating panels under the car to improve airflow and not running a splitter? Are pretty much all splitters really just cosmetic? Is smoothing out the underside of the car to minimize drag substantially better than bolting on a front splitter?