I like just converting to the mid-late 70's Ford Duraspark II ignition setup. All you need is the distributor, an ignition box, some wiring and an "electronic ignition" coil. For the very low budget this stuff can still be found in backwoods junkyards. Trucks, vans, Granadas, LTD's, doesn't matter. As long as the distributor is the correct one for the engine you're going to use. IE, you can use the same one for a 260/289/302 and even a 5.0 but not a 351W. The 351's have longer shafts and larger oil pump drives. Assuming you are going with a small block. Everything except the wiring can also be had at your local parts store. Just tell them you are working on a, say, 77 Granada and they will be able to hook you right up. Rebuilt Duraspark II distributors run about $60. Don't forget the cap, rotor, and wires. The wires for the old points type distributor won't work. It's usually best to refrain from telling the parts people what it is you are actually doing, you'll only confuse them.
It's not hard to make your own wiring harness. The last few I got from a junkyard had damaged connectors anyway. Crimp connectors wil work fine.
Another nice thing about the Duraspark setup is that you can buy an $8 adapter and any MSD fancy ignition box you like can hook right to the Duraspark distributor.
Here's a helpful link or two on the swap.
Basic Duraspark swap
Here
And dig around at this one, in the tech section under ignition AND under electrical. And yes, I know it's not Mustangs but still very good info.
Here
Restoring a 68 coupe 
