There are some details which could hinder the OpenVMS installation on a PWS 500au. Could be easier to assist if knowing what happens when you try to install OpenVMS.
The graphics adapter is not necessary for the installation. It can be done completely using the serial console (COM1 port).
Dear fellow hobbyists,
To answer the original question; I do have some DEChub 90 modules and DEChub 900 modules as well in my collection. Used to work with these a lot in the 90's and even early 2000's.
Great equipment at the time.
If there is interest, I can share information about and...