dual reservoir
It's a good idea, but a few details need to be addressed. Is your coupe power assisted. If so, the details are complicated since the original booster and a dual MC won't fit between the firewall and the shock tower. There are conversions that use more compact boosters, but they require considerable FAB.
If the coupe is manual brakes the job needs a proportioning valve and adaption of your existing hardlines. As posted previously a manual MC from a Maverick/Granada bolts right on and has the same push rod configuration as the original fruit jar MC. They are available new for about $45. Don't use a rebuilt one.
See member degins auctions on EBAY to see a full disc brake swap kit for your 66 which include everything from a new master cylinder to dust caps and everything in between except the hardlines for about $600.