Have you tried to adjust timing with a vacuum gauge attached the intake manifold vacuum-wiper port? Set timing to maximum vacuum at idle. That gets you close enough to run smoothly.
First, set timing mark for #1 cylinder at compression/firing stroke (at that mark, the distributor rotor should point to the #1 spark plug wire). Wires in clockwise order should be 1 5 3 6 2 4.
