Hello, everyone.  I wanted to ask about this to see what those who know more than me can say about what I must do.  First, I have a Polytech That was one of the ones caught in the importation ban, so it has a threaded barrel or front sight block, and it is one of the styles of sight blocks that are "longer," or cover more of the barrel behind it (hope this makes sense, as I cannot take a pic).  So, this sight block has a muzzle brake welded on to it.  Here are my questions:
1.  Is the barrel or just the front sight block threaded?  This will determine whether I have to cut the weld and remove the brake, or can just drive out the pins and replace the whole FSB without having to deal with getting the brake off.
2.  Is this older style of FSB still available from Keng's?  Their website only shows the "shorter version" of FSB that does not go back as far on the barrel as the type I have.

Thanks in advance for advice on this.

the barrel itself is what's threaded.  Just cut the muzzle nut lengthwise with a dremel a couple times and it should come off.  It worked on my SAR-1, which had a perm-attached muzzle nut added at my request by Troy at Inrange.    In my haste I dinged the threads a little, but nothing that impedes function.