LS1 swap in a 72 blazer making noise

ok so i bought an old blazer (my fav truck) everything in it is new but the body looks like a rat rod, Love it. my issue is that when it warms up it sounds like the lifters, rockers, or something is rattling when i accelerate. Any suggestions on what it could be? the engine is new as is everything under the truck, dude i bought it from didnt have the TCU set up correctly so i had that done. Just wondering if maybe the rest of the electronics are jacked as well or do i have mechanical issues in the head (241s) somewhere?