Sorry, I couldn't resist the "clot" bit.
Chip McCormick used to sell receivers but they are no longer listed on his website or Brownell's.
Exxex frames are cast. Recent production is reported ok but they are usually considered a step behind Caspian.
According to their www, the STI forged frame is not precut for an integral ramp barrel.
I have a couple of guns on Caspian parts that do very well. I have one on a Baer frame that is just as good but I cannot say it is better because it is forged.
What counts on a frame is that all the cuts and holes are right or at least usable and that you fit up the other parts properly, not where the raw metal came from.