Since I don't have a short block if there are any fitment issues then I will source a 2 piece rear main block and use that, but there is more of a selection and options going with a factory roller block.
I misread your original post. I thought you already had the OEM roller block. :-(
What kind of power are you looking for? For sub 500HP builds GMPerformance or Summit 4 bolt main blocks are a decent value. Clean, hone, install cam bushings and ready to go.