Easy... Standard three inch instruments, extrapolate the rest from that.
Smaller base measurement makes smaller gaps more "measurable" and you can avoid having to make the image bigger and risk pixelation. You could even measure it off your screen from the picture you have posted. It will always be hard to try to "subdivide" the large quoted figures to go smaller. As a rule, work from small to large and crosscheck with the large figure.
Oh..and don't get hung up on "exact" measurements as the R is different to the others anyhow. When you convert it to full scale, an inch either way will be completely unnoticable. That may be a little unpalatable but unless you get all the curves exact, the seat height exact, the distance to the panel exact, the rudder pedals and yoke exact....... What I guess I am saying is the Spitfire Cockpit is a 1:1 replica that has taken years..but don't ask me to list the things that are slightly "off"...and NOONE would ever be able to tell.
It does help to have been building cockpits for 16-17 years
