Huh, I had seen that 1983 manual but failed to notice it also mentioned the "+". Scanning the manual it seems like it's pretty much a 3A with the fuller keyboard and, well, that's pretty much it.
Sort of wish I could lay my hands on one of these to use with my NorthStar CP/M box, assuming I ever get around to getting that working.
If you are looking for a serial terminal, I may have a Televideo 925 to part with. Looks very much like a classic VT-100. I also some DEC VT-220s but I'd have to make sure I have a keyboard to send along.