I recently discovered some of the info I was looking for on a site:
MY OLDRIFLES. this shows pictures of a santa fe and it says that the santa fe carbine started as a No1 Mk3. the one I have is dated 1944 and is a SHTLE. the picture is very simular to the one I have except for the butt plate, mine is like the original No 5 with the right side of the butt plate that has an attachment for a sling. next subject: I was at a gun show and one of the vendors stated that there is a insert that can be put into the rear sight of a No4 Mk1, that would reduce the opening. does anyone have any more info about this?