i dont know which way to go for more hp....i want around 4 to 500....should I go with a crate 351 bored to 408.....or should i keep the 4.6 with only 64000 miles on it and put a root stlye supercharger on with pi heads, plus adding the 5.0 or 5.4 sroker bore kit you can buy for the 4.6......which route should I go

 

Steps:
1) Buy a forged bottom end for the 4.6
2) Add boost

There's not much more to it than that, the 4.6 can take you to 400-500 easily. 400 RWHP is ok on the stock bottom end even, pick up a centri kit for cheap, add 11 psi and you'll be over 400. If you want more than say, 450 rwhp, you should forge the bottom end, or it'll just be a ticking time bomb.

Edit: Forgot you said you don't have PI heads...

Add a step somewhere in there: PI swap

 

ok cool....the stroker kit should beef up the bottom end too

 

The 5.0 stroker kit is just fine, a good idea if you're going to be buying new bottom end parts anyway. Just be sure you're buying one with forged rods, forged pistons, and a forged crank. The cheapest stroker kit is likely to have near stock-strength parts that will fail around 450 rwhp!