Wondering about dimensions for barrel hole spacing for mounting scopes or rear sights - I found a picture in 2-clicks in the FAQs, looks like 1 inch (1.00) for rear holes and 1 and a quarter inches (1.25) for front holes on top of the barrel, (do not have an actual barrel with me now). Is that about right, (I haven't swapped sights recently)? I see a fancy English rear sight on line with 20mm hole spacing and guess that that would not work?