Hey everyone. I was just wondering if I had to use a PSA upper with the PSA 9mm lower. I am assuming that the only part from the "PSA upper required" line on their lower pages is the bolt cut for both colt and Glock magazines and has nothing to do with the upper reciever itself, nor the barrel and barrel extension. Ami correct in assuming I can buy brand X upper reciever, a PSA BCG group, and stick it on my lower and be good?