Mate, speak with your CALIPER SUPPLIER re the correct sizing of the mastercylinder you will need, piston area will determine what size is correct for it, once you have that there will likely be a "vintage style" but new and correct cylinder to suit those calipers, 5/8 would work but might not give you the stopping power you are looking for. You might also run into clearance problems wither your spokes with the inside of the caliper.
Cheers,
Kt
