1966 Rear shackle and front leaf spring bolt size question?

I am doing all new rear suspension on my 1966 mustang coupe.

Looking at the rear shackles for dual exhaust that are available on CJ pony. Some say 9/16 and some say 1/2".

I am pretty sure I need the 1/2" bolt size for the front eye for a 1966. But the rear shackles all come with 9/16 rubber bushings. Shouldn't it also be 1/2"?

Also. Should I switch them out for polyurethane?

Any suggestions/tips would be greatly appreciated.