I don't know what the front track is on a '66, but maybe this will help. I have a '67 Barracuda that I swapped front discs and an 8-1/4 rear from a '73-76 into. Since the '73-76 front track is wider than a '67 (nearly 7/8" wider on each side), I tried to make up for it with the offset on my wheels.
I bought Mopar Rallye style wheels from Specialty Wheels, in the following sizes:
Front: 14x6" with 3.75" backspacing
Rear: 14x7" with 4.12" backspacing
I mounted BF Goodrich Radial TA's, in the following sizes:
Front: 205/70R14's
Rear: 225/70R14's
Here's what it looks like:
Hope this helps.
Roger