Any 2 door A-body bench, 67-76, will physically fit. The catalytic convertor bump affects the bucket seat mounts, not the bench seat mounts. And other than the catalytic convertor the floors are the same 67-76.
Obviously there are different style benches over that range, so some of those years would have styles that were not available for a '71, and of course the upholstery style would be different as well. If you got a style of bench that wasn't correct for '71 you may have a hard time matching the cover to the rest of the car, if you're buying the seat upholstery to be correct for a '71. But it sounds like this is just a temporary seat, so it wouldn't matter then.
Heck even a 4 door bench would physically fit, but it wouldn't have the folding provision so you'd lose access to the back seat.
