The spare is a low speed smaller setup as Ray and Geoff indicate.
I'm running OEM Wheels on my 78 - steel rallies, c/w 255's.
These can fit in the spare carrier, since the bolt up bit at the rear can be turned 90° and dropped to a lower position.
AND.
The front two hangers allow the carrier to be lifted, unhooked and also dropped to a lower position.
My STD 255's just fit in, but once the carrier is tightened up, be aware that speed humps are a no go, since clearance now under the rear is very close. (The 255's are a bugger to get into the carrier, esp now I'm old and decrepid.)
Keep in mind that the carrier, cross member, diff/ axle and spare are designed as part of the rear collision crumple zone, and it is highly recommended that the correct spare fully pressurised with air is always in position.