So your dads sperm planed on building a mini truck for you? :crackup
:skid #1
Yet you are opening up the exhaust, installing a shift kit and putting a limited slip rear end in it to plant the power? Those are PERFORMANCE improvements, aka you want it to be faster than it already is. :skid #2.
You dont need aftermarket support to make a fast truck. Its about the simplest designed vehicle out there! The $500 you are spending on dumb 3.0L shit, would get you a wrecked 5.0L mustang to pull just about ALL the parts off for a swap. The truck itself is a frame suspension and a seat… thats all you need.
That thing will never be slammed, low. The geometry (as you know) doesnt work anywhere near today’s standards of “low”. Put drop coils in up front and shocks to match. Get about 2.5" out of it and be ok on the stock bullshit arms. Out back. I havent looked under one of those old trucks in a long time, is the axle above of below the leaf spring pads? If its below, just flip it and put eh axle above the leaf. Right way of doing it is cutting the pad off the bottom of the axle, and welding a NEW one (15$ ea) on the top of the axle in the correct position. U bolt it on, BAM 2.75" drop. If you need more, 1" block. Dont go nutty and put a 5" block in there, axle wrap will be bad. Max 3" on blocks IMO.
Anything lower and you are into mustang front suspension swap to do it right. AGAIN, buy a donor 5.0L and you have everything to do the swap for the most part, motor, trans suspension, etc.