I have a .750 and .625 AR15 sight tower/gas blocks. What I need is a .875 size gas block. If anyone wants to trade a .875-.900 (not .936/.937) gas block for the two gas block/sight towers I have, please email me. One of the sight towers has the sling swivel on it, both have a bayonet lug. Neither one has a gas tube. Used but serviceable is OK, prefer blued/black. I'm in the Portland metro area.