The 17 digit VIN should be right if its post 1981. I know the R-series trucks were mid-late 60's to early 90's production so I really wasn't sure what to expect in terms of VIN # format. I'm not near as big into TT stuff as I am older Ford/GM/Mopar stuff..
I'll have some time later this week to photograph his vehicles, gather more information from him, and do some more research on the truck itself, as well as a few other vehicles. I don't think the old Mack has seen daylight in quite a few years, as with the rest of his collection.
The Museum is closed still due to COVID, but at your advise I did send them an inquiry via the contact us form, so we will wait & see what they have to say. I have also reached out to one of my good clients that works for Mack & provided him with the info I currently have as well.