rear drums question

[of13swc]

Ok well another o crap look what I found. the drums on the rear of my truck (1965) they are supposed to be 6 lug. But mine are 5 lug. So the truck was changed, my problem now is where to get rear drums for the truck. The ones now need t be replaced but don't know what to order. Any suggestions? What was the original drum size? Or how do I measure the drums now so I can look for the same size with the same bolt pattern.