[p00t]

Likely that is your culprit. Basically a yellow or orange spark is very cold (in the world of sparks). Since you've changed the wires and distributor already the only item left is the coil.

You can check coil positive with a multimeter but the ground side thats controlled by the transistor needs a scope to diagnose.

If you have a spare coil and transistor or if you can get them on loan try them out in the car. The power and ground can be back probed to + and - also to ensure there is no issue with corrosion of the wires.

Good luck!