Normally, 15" wheels are required. From the VCTI forum:
Allan and I collaborated to put together this guide based on our experiences installing the ACC Disc Brake kit. It's mostly his work with some added photos and comments from my installation. Tom (ABQTbird), the moderator of the 1961-1963 Thunderbird group, agreed to host it on his website. It's downloadable in .pdf format, so you can print it out (49 pages long, though) and take it to the garage or driveway if you are installing this kit, or any of the similar kits that use brackets made for stock spindles and GM floating calipers with Granada rotors.
http://home.comcast.net/~rt66tbird/w..._Kit_Guide.pdf
As stated in the introduction and in my previous posts on the subject, this is just one option for installing front disc brakes on a Bullet Bird. After reading this, you may decide to go with a different set-up. But we both definitely think that if you do use this (or a similar kit), the job will be easier and you will save a few dollars by getting the right parts.
Let me add that my wife and I are BOTH very satisfied with the results and feel our car is much safer to drive in traffic than with the factory front drums.
Hope this helps anyone looking to upgrade their brakes!
Dave