I still have the glossy printed instrument faces that MICK REEVES supplies with his CAMEL and PUP plans. These are 1/3rd. scale so you will need to enlarge accordingly--
'SMITHS' AIR SPEED---1 and 5/16ths.of an inch.
MARK V RPM-----------as above
'OIL'-------------------7/8ths. of an inch
Service watch---------3/4 of an inch.
'TYCOS' Altitude -------1 and 3/8ths. of an inch.
All the above at 1/3rd. scale remember...

and only 'face' measurements---add for rims.
Dave. Edit----Mick is a designer and flyer of magnificent scale Sopwiths, so I don't doubt the acurracy of these Des.