So how do you know it "puts down 430+hp"?
What year Transam 400? Is this a Pontiac engine or a 400 small block Chevy?
What exactly is the problem you are having?
Is the cam too lumpy causing drivability issues or is it just a traction problem?
If it's a big rough idle cam and you are having a problem getting the clutch out (you didn't state if it's a stick or automatic) you may need lower gears, a posi will help with traction but won't make any difference if it's a big cam and too tall gears making it hard to get moving and if you launch hard you'll have to be on top of it because posi can get you sideways real quick if you are spinning your wheels and not ready for it.
Not enough info here to go on,we need to know what the engine is and mods if you can find out, what tranny you have, what rear end and gear ratio it is and just exactly what the problem you are having with it is before we can offer a solution.

 

 

Well learn to control your throttle. All else fails take the 400 engine out of the car and put a stock 170 HP engine in the car. There are just those people My friends and I have built for customers .Who are used to driving lesser power car. And when they get into healthy car.They just can`t handle it. I have driven all sorts of very healthy cars .And have a 1979 Z-28 RS Pro-Touring car With a 500 HP supercharged small chevy. When I first driven the car.I just apply the throttle a little at a time until I got used to it. And learned how to control it. I have an advantage over some people because I have had drives training for a CDL license. Maybe some sort of performance driving course might help you.

 

Ok so it sounds like mostly a traction problem, a posi rear will help and you might want to look into some good sticky tires. Tires alone can make a huge difference, with good tires and a posi rear you'll launch instead of spin. Traction bars and sub-frame connectors are other things you might look into.

 

maybe , your throttle linkage is sticky, you should not drive it until that is remedied. if your throttle or pedal got stuck turn off the key but not all the way because you must still steer. turn the key off enough for the engine to shut off power steering will NOT be operational but you must NOT lock the wheel to steer. this would be classified as an emergency situation. you do NOT want those on the road to EVER happen. you could sell your motor with a dyno sheet. or dyno the car as well. then buy a gm 350 vortec. but you definitely need positraction. or limited slip differential, its called LSD. ilike both lsd and posi. positraction is a great rear end. it uses clutches to push with both tires. without being completely mechanically locked. this is safety and drivability. traction= SAFETY. as well as performance.
It may be that the engine is very powerful and it sounds as if it has a 5500 stall converter too high really for street.
it also sounds like maybe it was a race car. it also sounds as if it has a spool or slick drag racing tires. and a drag race suspension. maybe you do not sense when the torque is overpowering the tires in your throttle delivery with the pedal. do not give it that throttle. Sell your car if you feel your safety is at risk. or you can change it. you can put a mild engine in it and at least add a limited slip or posi unit. if this car is not controllable don't drive it. it could be broken. sell it to someone on here or we could really find out what the problem is and help you. but you got to try something. taker easy, and be SAFE.