I have a '66 Restomod coupe with Granada spindles and discs on front.
These work OK, but won't fit stock '65-66 styled steel wheels. I had steel rims from a '68 and they cleared fine - just had to get the rotor center hub turned down to fit the smaller hole in the wheel - Ford switched from 2.4" wheel hole to 2.7" hole in the early 70's - so the Granada rotors have a larger center hub diameter and won't fit earlier wheels without turning it down smaller. You should have no issues clearing aftermarket wheels or later model wheels.
Granada discs are probably not as good as the later model 'stang Cobra brakes you can retro fit. Go to http://www.mustangsteve.com for details on using Cobra 13" or 2005-up 12.5" front discs on your stock spindles - but you will need 17" wheels.
I have all the pieces to put rear discs on the '66 too - just haven't done the work yet. These will also clear the stock 14" rims with a small spacer - I've mocked them up using a 5/16" spacer and they clear the rims easily. You will need longer studs - I can give you the details and photos of what I'm using if you send me an email.
Basically you swap late model Town Car, Marquis, or Crown Vic rear discs on to the 8" or 9" rear housing with a slight trim of the axle housing mounting plate - in place of your original drum backing plates. You also need some large washer type spacers to keep the axle and rotor properly positioned. All total I have less than $400 in this swap - and the master cylinder, rotors, calipers, hoses, and pads are all brand new. I got all the used parts at Pull-a-Part for $75 including the parking brake cables.
Check out eBay item # 370329407117 for details on this swap. This guy is selling the spacer rings you need along with detailed instructions. He was really nice to work with and shipped my spacers really fast.