With a look at my 2018 Plus4 there is a simple rule:

Engine and gearbox are Mazda, so metric. The rest is Morgan = imperial. That would work for a mainrule at a modern car. But there are some points with riveted and pressin nuts with metric M6 (for 10mm spanners).

Also a point: if a car gets older there are a lot of wizards around which cut and change things Just for their taste and work.

Greets René

So both worlds of spanners would be a good idea.

2018 plus4 (sports green)
with a homemade really shiny red tinted dash…