Tyres.... sorry Tires question

To determine rim width you will need to pull a tire off (unless it is stamped by the valve stem)

My 67s are stamped on the inside of the rim, later 68 up seem to be stamped by the valve stem.

Either way measuring from inside bead to inside bead will tell you.

Other tattle tails is the back spacing.

I have one of each here and can get you the numbers.

Also some tire shops have a caliper that they can measure the outside of the bead to the outside of the bead, they might be calibrated to remove the steel wheel thickness but if they are less than 5.5 outside to outside assume they are 4.5

Other tattle tails would be if they came on a slant 6 car, or a car without front disc brakes that might indicate 4.5.