There will only be a single ignitor circuit in the Crane unit, controlled by the chopper in the distributor...solid = points closed, gap = points open. Is the chopper the correct one for this distributor, as it has to maintain the relationship between the rotor position and the crane unit firing.
You can connect the timing light to cylinder 4 with the engine running, and it should fire at the same timing mark as cylinder 1. Then make a mark (chalk) on the pulley 180 degrees from the TDC mark (ie diagonally across the pulley), and connect the timing light to cylinder 2, then 3, which should both be firing at the new mark. This will verify that the Crane unit is firing at the correct timing.
Then set the engine to TDC on no 1 Cylinder, remove the cap, and check that the rotor is pointing directly to where the pickup for NO 1 cylinder should be. There should also be an opening in the chopper passing through the optical sensor. If the distributor is not phased properly, there is a remote chance that it is cross-firing when you retard it. This could explain cylinder 3 firing intermittently. This is more of an 8-cylinder problem, and not really likely on a 4 cylinder, but worth checking.
TR7 Convertible
Sprint Motor
MegaSquirt EFI
