Is this a good donor car?

That would be a great parts car if you were doing a '68 Dart.
In my opinion, you should find a '73 and up a-body V8 car complete, running, and driving and use that instead. Something a little rusty and dented up with a thrashed interior would be perfect.
Then you'll have the good big bolt pattern disc brakes, the good spool mount k member, and bbp rear diff, electronic ignition wiring harness, etc. All of this stuff is a direct bolt on for your car.