Stock Wheel Width for '75 Swinger
If you can measure the outside where lead weights sit to same on inside. That will get you a number that will be close enough to determin if they are 5.5 or 4.5.
Any tire store has a caliper to measure such
I'm betting 5.5 as well
I saw somewhere that some of the steel wheels had the dimensions stamped into the outside of the wheel near the air stem