Not really a bodge, but if Caterham USA fail, maybe try a local parts factor for a caliper from a Merkur XR4Ti or Merkur Scorpio. I believe this was the regional branding for North American/Canadian versions of the Ford European models.
Jon,
trust you are well.
Have you re routed the centre ht lead at all? Or is it in a poor state?
Trish's SLR went through an odd spell a few years ago when the lead was repositioned closer to the crank sensor on the back of the flywheel. It appeared to be a noise / interference issue. Routing the lead further away sorted it.
Some of the standard Rover induction manifold types have a form of 'jiggle valve' fitted in the port which feeds the small line to the expansion tank. Designed to allow air to pass through but block the passage of coolant. They can also sometimes stick.
It is a while since I walked the course or received the Drivers' Briefing at Curborough and photos from the viewing areas do not make it at all clear .
Is there a white line denoting the edge of the course at the inside of the kerb at molehill? Or does the kerb constitute the edge of the course?
[Runs away to a safe distance before the fight starts ]
Blatmail your address if you need a scan of the Metro manual.
There is also typically a ballast resistor in the form of a resistive cable buried in the loom, check you have got voltage when the key is at crank and run positions.
Is it the OE electronic distributor from the '80s? Metro Haynes manual has quite a few pages on electronic distributors but there are a multitude of types listed.
See if you can find the model code on the body of the distributor eg 65DM4.