You would have to research average European size since 1900, as that will give you the soldier's sizes too. From memory the average WWI
British
Soldier was about 5'2" and the average upper class, due to better diet, about 5'6". IIRC the average upped about 2" in WWII.
Lee Enfield butt sizes also give you an indication, as the L butt is usually too short for us. The S is really short.
Uniform sizes also give some information. Specifications for vehicle development might also be helpful. I know when South Africa started building armoured cars based on the
French
Panhard we lengthened the front by some half a meter to fit our soldiers.