Here’s a complete printset of the Venus Ibox, from 1984. It includes Ibox block diagrams, module and MCA block diagrams, and schematics for the MCAs and modules.
I’d bet my bottom dollar that there were ECOs after this version. But this hardware ran VAX/VMS and oodles of software.
Most of the page tops are faded. 75% of it is due to fading in the originals, and 25% is due to less-than-meticulous copying by FedEx.
Seek Nuance 
A friend of mine has acquired a VAX 8600 and needs as much detailed information as possible to get it running again. Your IBOX print set is of great help, but print sets for the other boxes (EBOX, MBOX, FBOX) as well as for the modular power supplies (MPS) are needed as well.
Can you help or do you know someone who possibly could?
Thanks,
Ulli
I don’t know anyone who has them, sorry.
https://www.vaxhaven.com/images/0/04/EY-4818E-PP-0001.pdf has some overview information.
Bob Supnik might know someone who has them. I don’t have his email, but he’s at https://www.linkedin.com/in/bobsupnik/ . Maybe send him a LinkedIn message.
Another possibility is Tryggve Fossum, https://www.linkedin.com/in/tryggve-fossum-0825036/ .
Good luck!!