My 2001 Caterham has a similar mix of threads - old chassis design, with modern, metric drivetrain.
Mind you, out technical manager decided our new machine 20 yrs ago would be UNC/UNF as it's main market was expected to be the US. Most of the machine is indeed those threads, but some proprietary items can only be had in metric - so some components have a mix of thread forms. Never mind the pipe thread issue . . .
That meant service engineers now had to find and carry basically twice the tools, our machine shop had to buy new toolings, both having chucked imperial stuff years before when we went metric.
As most of those machines have since been sold in metric-land, I'm not too sure it was a sound decision, especially as metric is now so much more common in the US and doesn't scare the plant guys.
Rover used unc, unf with metric (10mm) heads on the mini and metro, and metric threads on the rest (of the metro but not the mini). Story goes that when ze Germans went to look at the Bini they were horrified to find this was still going on...
