Compression

Last of the checks post the overheat;

Compression test is giving me around 175psi on each cylinder; no obvious low pressure cylinders so I think that is a good sign.

Spark plugs look clean too: for reference after 5,300 miles - in cylinder order 1,2,3,4:

Running the car up to temperature before the compression test also allowed a check on the coolant - nothing out of the overflow - so the new cap seal work has made some difference. Also procured a 20psi cap and comparing with this I think my original kit one is more like 7psi anyway; the new 20psi cap has the same issue though with the thermostat casting - it won't quite reach the shelf inside and will need the same extra gasket mod.

I'm going to continue running the lower pressure cap for now, need some more runs to test before I change things again.