Oh, that's interesting info. The Ford parts book had nothing listed for the GT 350 -
Ford "sold" a standard assembly line, stripped down Fastback to Shelby American in 1965 and 1966. That's why there is no listing for GT350s in those years. Special order components were listed on their build sheets - a rare find for almost all San Jose cars.
I also made the assumption that there may have been a late year change 4/15/66 as indicated by generic suppliers that there was a change. I assumed 65/66 was 29/32 and it changed to 7/8..
The 60-68 Ford Car Parts (aka MPC) sect 22 pg 11 (for base number 2261-62 - rear cylinder) shows a change over date for V8 rear brake cylinders from 29/32 to 7/8 inch on 4/15/66 for 1 3/4 inch shoes.
Remember, the MPC is a dealer
service replacement document and may or may not, reflect assembly line use. Implementation dates have also been found to be "flexible".
Jim