I'm not so sure about that. This would be the "midsize" wagon similar to the regal and cutlass wagons of the era. And I think they have the same track width as our cars, so if they had the 8.5 10 bolt, we'd all be yankin' them things out of every wagon in the yard. After that, I think the 8.5 10 bolt was only 84 and newer, hence the 83-back turbo cars and hurst olds had the 7.5. Again, I'm not "sure", but I don't think that wagon has the 8.5. I'm on the hunt for a clean wagon, been watching this auction for awhile now but I think the reserve is probably above what it's worth.
Now the newer electra estate wagons, they might have an 8.5 but they are wider I think.
my friend had a 89 or 90 buick wagon estate and it had an 8.5 im sure my friend has the 8.5 but i dont know about 79 i'll do some research get back to ya