You might check the archives and see what info is there. I have no experience with 17s on that body, but 265/50 fronts & 295/50 rears on 15x8s with 4.5BS fit my '68 RR with plenty of room to spare at stock height. A 10x15 rear wheel needs 5.5BS. I've seen 305/50R15s on the back of a '69 RR that still had some room, but can't recall if the guy had 9" or 10" wheels.