What's the chance this two-hole sight on the bottom left will fit my 1919NRA
Great, if you only use one hole! I wasn't sure but it looks like a sight for the later Remington model 121's & the 572's & possibly a few others.
second photo, lower right is a Marbles 95 and was made in different heights...is there a code letter stamped on it?
They were made in three heights and with the small sliding adjustment one of the three would work with almost any gun so there isn't a specific code stamped on most of them - the only versions that might have a code would be the ones with special bases - they were also made with a narrower dovetail for early Stevens rifles so measure the dovetail) and with screw on bases for guns like the Remington Model's 8 & 81. The XT, extra tall, I believe is only cataloged for use on the Savage Model 1920 and I don't believe they have a code on them.