Hi Will and All,
You are probably right about R8 tapers - it is common for the smallest horizontal millers to use a 3 or even 2 Morse taper, however they were replaced by int30 or int40 on later versions - note mine's an in30...
R8 usually means Bridgeport - they invented the standard - usually for their vertical quill machines - I don't know whether they ever did a horizontal with an R8 drive, but they did make a right angle drive and 'over-arm' support kit for simulating a horizontal drive on their vertical milling machines - Vertex certainly still make a copy of this conversion kit for int40 drive machines - I have one with the idea of using it as a vertical quill on my horizontal miller. The short stubs would make sense in their vertical millers using slitting saws.
Lovely pictures you've found there - that Elliott could be a similar model to my 181 - the top one's a beauty - with a double round bar over-arm - a bit big for my work-shop though!
Regards,
Denver.