I put one on my No 1 375 H&H, and had to get the high front sight from NECG. Works great, can clover leaf them at 50 yards, am thinking really hard about them for my 77/357 and 77/44 carbines.
for those wanting a photo of an NEGC on a #1, here one i took a while back:
re: the XS peep for the #1 - it requires you drill and tap. no thnx.....
re: skinner - i sure like the slim and trim look. and it doesn't require alteration to the rifle. might have to try one. even better, it also comes in stainless to match my #1S 45/70 stainless.