If I was going to nail down the issue, I would take the head off and remove the caps from the crank and take the pistons out. Check to make sure the crank can spin freely with no issues. While there are no pistons in the engine I would check for roundness in ALL cylinder bores. Also check your connecting rods for straightness. Are you using ARP bolts on the rods? If all is good there then reassemble and really watch your tq values. If over tq'd the crank will be hard to spin. Once you are have it back together, give the crank a few spins - check to make sure you are not hitting the casting on the inside of the block. Was there any metal or shiny oil when you just pulled it apart?