Maybe I'm not understanding what you're trying to do, but if I read your notes right, you want to build a preban version of the Galil in 7.52x39 caliber. So why not just buy a preban Galil, and have it rebarrelled to 7.62x39? Other than having a 'smith build you a 7.62 barrel, which could be cut to the exact Galil dimensions, all you'd need would be an AK bolt assembly, and installation of the flash suppressor for the 7.62x51 model Galil. Seems like this would be a hell of a lot less expensive than altering a Poly Tech Legend reciever, which would take extensive machine work; not just threading the barrel hole, but reshaping the bottom of the front end, and redoing the whole rear end for the Galil stock assy.
But maybe I'm not reading what you intend to do correctly.