I have no experience w/Kentucky Mustang, but I REALLY like dealing w/Brant @ Virginia Mustang www.virginiaclassicmustang.com
A ton of parts from him are on my old R Code (sniff), the '66 Mustang, and (at some point) on my '67. Check out his disc brake swap kits, note the differences in the parts spec. Delivering a kit at a certain price point is important to some vendors, but you ultimately bear that cost, because you have to live with it.
WCCC is 1st rate as well, but on certain parts I buy East coast as not to get killed on the shipping.
I gotta chime in for Street or Track here. Owner knows and races vintage Mustangs and has a great reputation amongst the track guys. Great guy and solid support. Can recommend them highly enough!
Took your advice and ordered a kit from them, as well as a new set of wheels as the ones that came on the car are a hodge podge of 3 different things with rotten tires on them so pretty useless.