Just thinking here, So bear with me. I have a POF Piston upper (one of the first few made) Anyway, Its a M-4 with the heavy ass "PREDATOR P-4X" Rail system. What's your take on cutting this barrel down to say a 10.5 or 11 inch barrel and making this rifle into a  SBR??? I'm really thinking about taking this heavy ass rail off anyway. And just going with a tandem rail instead of the Quad. Let me attach a pic to show what the barrel looks like. at the 10.5 and 11 inch length.

Not knowning how the piston would work by shortening the barrel, And would the barrel need more work than just cut and threaded there where the blue tape is at 11 inchs?? And do you think i should have ADCO or someone like that do this or maybe even have POF do it. Or just scrap the idea and build another non piston SBR or save up and go POF or LMT or someones Piston System..   Oww the pain in my brain........HELP

Those Mike Rock barrels are very nice and expensive to get. I'd sell the whole thing off if I was you and start over. You should get a pretty fair price for the upper.

Build a new upper.

^ this

Form 1 the lower as an SBR and build the short upper from parts (or buy a kit already in the SBR length you want).
I'd leave that particular upper as is.