I used to have a 70 GMC with the 16.5" steel wheels. Tires were a challenge to find so I used steel wheels from a 72 to 87 GM truck. I think they were 16 x 6. Those are out there you just have to be patient.
I also bought a set of Ford Accuride's that came on the late Trucks and Vans and those are 16 x 7 with 4" back spacing but they are not hub centric and yet many others use them. They also have the nubs for a hubcap should you decide to use one
I found this one available on Rock auto which is a refurbished unit for a 1993 G30 Van, and it is hub centric
https://www.rockauto.com/en/moreinfo...t=7644&jsn=892