but it has the old 9 pin D-sub connector which would seem to indicate it's CGA or EGA.

Click to expand...

... or TTL variant, MDA, Hurcules, or ... my head swims at lack of video standards before 1990.

Seems like you could best use the adapter. I'm starting to think the best thing for me to do is look into building a custom TTL adapter and D/A converter to get it up to a VGA standard, which is the ultimate goal to use contemporary monitors.