Forgot to reply but I got another scan of the manual that includes these scans from the person that gave me the crts. https://i.ohaa.xyz/raw/oRiMLv.pdf
Thanks, I really appreciate your detailed answer.

VGA might be a good idea. Do you think that these are just regular 640x480 displays? Can I damage them with a wrong resolution?

While I know(at least to some extend) what I’m doing, I still appreciate the warning. The Monitors.only interface seem to be these Pins labeled J1 in the Manual.
Heres a picture of the entire Board in case that helps:
(I know, that brown discoloration looks horrible but it still generates high voltage and makes that high pitched crt whine)