Using mustang rotors for 4.5" bc

I have KH on my ragtop so I have the original BP. If I was you I would sell the KH set up and buy the (73 -76?) dart disc brakes. You would probably break even or even make some money if you sold the KH parts individually Hubs are harder to come by as well as Calipers JMO
If I could find a bbp setup locally then I'd probably do it. Shipping into Canada will kill any good deals from the US. Places like Pirate Jacks etc would be even more. I do want to stick with a factory brake system. Aftermarket stuff is even more money, not worth it imo.