The Bomar sight for the MKII requires milling anarea for clearance for the bottom of the blade. You have to mill off about .030" in the area that the retaining pin goes through. You then have to file off the top of the retaining pin to match. The Bomar rear sight usually requires a slightly taller (about .050") front sight. They sell the front sight for the bull barrel MKII's along with the rear sight if you so desire. They are a pain in the butt to install but the Bomar sight is the best there is. Great sight picture, absolutely precise and repeatable adjustments. The Volquartsen sight for the MKII is a close second. The blade is slightly smaller so the sight picture is not quite as good as a Bomar - it is still a lot better than the factory sight picture. The adjustments on the Volq are, likewise, precise and repeatable and they are pretty much a drive-out drive-in in replacement for the factory sights.
I've got both sights mounted on different MKII's - the Bomar on a 6 7/8" Tapered target model and the Volq on a 5 1/4" tapered bull. Both are substantial improvements over the factory sights but for pure target shooting (bullseye) the Bomar sight picture is the better of the two..