On the 1st EB I owned (‘72 wagon) with an aftermarket swinging spare mount, I had a 33 12.50 15 mounted. The first time I swung it open, the fender flexed enough to make me take the mount OFF and put the spare in the bed. I’m sure the OEM mount is much better secured to the rear quarter panel but I wouldn’t trust it. Just my $.02 worth.
Randy
Randy