Yesterday I sent the seller an email inquiring about whether it was the
factory sunroof or an addon.
I got a response earlier today.  The person listing the van is the son
of the owner and he told me that it was not the factory roof, although
he could not tell how big it was or who installed it.

Sam Walters
84 Vanagon, original owner
89 Syncro GL - has not heavenly body type hole in its roof at this point.