Heres an idea; source a machine shop that sells exchange engines.Ask them to piece a vortec engine together but use a 3.62 stroke crank(stock GM 6 liter) a 4.03 bore. Buy a set of modified vortec heads from a reputable dealer like scoggin dickey. Use a 450-480 lift roller hydraulic cam around 224 ish duration and what ever bolt ons you like.
Drive the truck,,,,,
the engine will make 400 hp plus or minus,will rev freely to 5500 plus RPM,have a nice power delivery and very responsive.
To make more power,expect to spend a lot more money. Quit looking for some super deal in a forgotten barn,just get what works and doesnt cost much. If you dont abuse the engine,I see no reason to buy forged pistons or floating pins etc. DO: balance the engine!