Edit: this isn't quite what you wanted, but it's a way to get modern brakes onto your classic. These are the only actual drawings I've seen on the forum.
Do a search for PBR calipers and you should find it. The only brackets that I've seen drawings for are brackets that allow the '99-04 GT and V6 front calipers to be used with Granada spindles.
http://forums.stangnet.com/showthread.php?t=502531&highlight=pbr+caliper
There's the thread for doing that. I like the idea of an adapter for '70 drum brake spindles as well, but those brackets are a lot more complicated. I think the PBR calipers could be mounted on Granada spindles by anyone with a welder and just a few hand tools. I plan to do the PBR calipers on my '70, which has the Granada brakes right now.
Edit, one other thing. I don't really like the idea of mounting the caliper to those holes that are sized to hold the backing plate in place. Yeah, there are four holes, but they aren't sized at all properly. Compare them to the size of the holes in the caliper itself. Now consider that the caliper has a longer lever arm, so the force is multiplied at the location closer to the spindle. They are also coarse thread. I suppose the spindle could be drilled and tapped for something about twice the size, and that could do a great job of keeping the caliper from tearing itself loose. I wouldn't publish a drawing of a bracket that used those holes as is, even with disclaimers.