Technical Starter not engaging

[bugsymike]

Took off the Ford one as I thought it was different but it's identical - refitted the Ford one. Used a borescope to check alignment through the bell housing inspection hole and it looks close enough. As I said hitting the starter signal connection spud with 12V directly from the permanent 12V connection from the battery turns the engine over (pulled the fuel pump fuse to stop fuel spurting everywhere). But trying to use the key in the ignition with the signal ring refitted produces the clicking in the fuse box. Same clicking when I reassemble the intake manifold, ignition coils. et al.

Have had people get a poor electrical connection at starter terminals both main and solenoid, sometime trapped between plastic etc. on solenoid.
Minor detail, but I assume donor engine turns over freely by hand with socket and ratchet on crank?
So when bench tested the Ford starter, by power to main lead and battery earth using jump leads etc that on powering the solenoid the starter the pinion engaged and the starter span fast?
Ruled out by using donor flywheel and starter, but I have had different number of teeth on starter cause issues in the past.