Re: hp gain?
If you go the complete...full out...long block with all the goodies you can get up into GT hp range...
But, as stated above me...just go GT because you will be looking at ~6-7k plus labor to do it right and then you will be maxed out. A GT will be a touch more but you will be at the bottom of the potential with room to grow. IT is a better base to work off of.
"When I know more, I'll be forthcoming. Or I won't be forthcoming, and I'll be honestly deceptive." - Les Miles