Extracted from the 60-68 and 75 editions of Ford Car Parts (aka MPC):
Front Sway Bar: (All numbers are service replacement parts. No dimensions were shown, except as noted.)
C5ZZ-5482-B - Standard, all.
C5ZZ-5482-A - GT/HP (aka Special) (75 MPC - 13/16)
Sway Bar Bracket: (Two required)
C3DZ-5486-A - All
Insulators: (All numbers are service replacement parts. No dimensions were shown, except as noted.)
C4DZ-5493-B - Standard, all (Also used in 1967)
C5ZZ-5493-A - GT/HP (aka Special) (75 MPC - 13/16)
From all three of my current Mustangs, 65 GT Fastback, 66 Hardtop and 66 GT Fastback HP, all have 1 1/2 inch wide brackets. All are San Jose built. As far as I know, the 65 GT Fastback (purchased 1993) and 66 Hardtop (purchased 1988) have their original sway bars, insulators and brackets. All I did was replace the end links.
The 66 GT Fastback had the entire front end "reconditioned". After that process, I put the original brackets and hardware back on.
I have a GT/High Performance 13/16 inch diameter sway bar I got several years back from a Mustang shop that closed. The two insulators are still on it. They have the "telltale" raised ridge from the brackets imprinted in the rubber, but the imprinted marks from the brackets are 1 1/4 inch wide. What do I have?
Jim