Actually I think the boat tail Rivvies had the larger 5 x 5" bolt pattern. What you want would have come on higher optioned late '60s to mid '70s A bodies, as well as '77(?) to '84 LeSabres, or whatever years they made that body style. To my knowledge, the brake clearance issues were with the more common 14" Rallyes on the late '60s A bodies before disc brakes became really prevalant. My '78 Sport Coupe came factory with the 14" Rallyes, so clearly brake clearance was not an issue. I believe someone on V8Buick.com is selling a set of the 15s right now, might head over there and do a search.
Option two, I could give you the number of a guy in Slater, Iowa that will take 14" wheels, cut the centers out, and re-weld them into new 15" shells. The 14" and 15" Rallyes actually all used the same center; only the rims were different. The guy who did mine can also do custom widths and backspacing as needed.
Right now, I've got 3 Rallyes off a '77 LeSabre, and 2 are the reworked ones that he did. He's also happy to buy cores if you have extras laying around like I did. Between my Sport Coupe and years of junkyarding, I had a total of 11 wheels to trade in, so I got a heck of a deal.:wink: