what does it take to upgrade a stock engine for serious boost

If you change out the stock pistons and rods for a set of forged and a steel crank...
You'll be set up for as much HP as you want to make.

yea you will have to do rods crank and pistons...so if you go that route you might as well make it a 302 stroker since you are spending the money you will be much happier and the power will be much stronger....alot of compaines do sell the short blocks for a fairly decent price then all you gotta do is bolt your stuff on and go...

500 hp at the crank?? That's not alot you can get that with any decent blower kit and your stock motor should be fine provided the tuner is good and the A/F mixture is on the money. Vortech, Procharger, Roush Saleen, and Ford Racing have kits between 450 - 550 HP at the crank I'ld start with that first the motor will last even under moderate "beatings" and I'ld worry about a block when and if yours blows. At that point you get the FRPP 3v SC block.

If you're not going FI then a nice 331 stroker motor will be an ideal choice, Check D.S.S. (i've purchased a motor from them excellent) Livernoise etc... The current MM&FF magazine has article with a bunch of good engine builders.

Depends. There are plenty of guys running 500 rwhp with stock internals. There are plenty of guys who have blown up the stock motor with only 400 rwhp. It's a crap shoot. There are way too many variables to say. The rods are definitely the weakest part. If you want to be sure you're not going to blow anything up than you're going to want a new forged rotating assembly. It's going to be around $2,000 for new pistons, rings, crank, rods plus the cost of the power mods.