Pre-war ES2 rims

So, there I was, poised at the keyboard, about to order the new rims for the '39 ES2 I'm restoring. The bike is currently fitted with 19 inch front and rear. The options from the supplier include a 21 front and 20 rear. So, I decided the best thing was to double check. Out to the garage, comparing the mudguards with the wheels, hmm, radius of the 'guards is slightly more than the wheels as far as I can see. The garage is a bit crowded, so may have to double check outside tomorrow, but can anyone tell me what the catalogue size actually was? Have looked everywhere, and can't find a definitive answer, the late '40's parts book says 19 rear, but on the front, only says 21 for Inter, doesn't give the size for the other models, they simply have a different part number. Also, it was quite common to have larger wheel sizes pre-war, so don't want to rush into it !

Cheers, Tony.