Will the '68 Dart 225 run again?

I'd be actually checking spark at the coil. Also, rig yourself a nice big (no 14) clip lead that will reach from the big stud on the starter relay over to the coil + terminal. Clip this on when ready to try it to insure you have good ignition voltage. Do NOT leave this connected for minutes on end while you "scratch your head"

You may have a timing chain issue. Have you run a compression check?

Where is the timing set? You can check it "on the starter" if you have a good battery