That's a good thread Tom, except it has your wheel info WAY wrong.
0 offset
I had -12mm offset on a 9" rim and it wasn't even close to yours.
I think yours is two parts:
1.) very negative offset: maybe -20mm or more
2.) very wide rim: 12" possibly
These two things create the phenomenom we know as the "offset from Hell"
Sorry for the TJ.
I have no clue on the specs for my rims. The PO put them on & there are no markings on them anywhere. If I ever put a matching spare on the 5th rim, I'll try to take some measurements. They probably are 12" wide though since the tread width seems the same as the rim.