If you've got the ball on the flywheel cleaned up and painted, it should be a simple task to turn the flywheel until the ball aligns with the pointer and check to see which spark plug wire the distributor rotor is pointing toward. It should be #1 or #6, as the engine turns twice for every turn of the distributor. You can use either spark plug with a strobe light to set the timing. The flywheel bolt pattern is almost, but not quite idiot-proof, as the bolt holes are not perfectly spaced. A sufficiently persistent idiot could probably install it wrong by not using all the bolts, but there would also be a massive oil leak through the hole for the missing bolt(s) as the bolt holes go all the way through the crankshaft flange and a leak can bypass the rear oil seal if they're not all there.
Jerry
