The neatest solution is just to buy 2 modern front brakes. Fit one to the rear with a standard nyloc nut, drill out the back of the fork (dead easy) and fit the other to the front with a recessed allen sleeve nut. Sell your current brakes on here to recoup some of the cost!
Edit: although recessed allen bolt fitting brakes are a pain in the arse if you want to take mudguards on and off over the course of the year.
The neatest solution is just to buy 2 modern front brakes. Fit one to the rear with a standard nyloc nut, drill out the back of the fork (dead easy) and fit the other to the front with a recessed allen sleeve nut. Sell your current brakes on here to recoup some of the cost!
Edit: although recessed allen bolt fitting brakes are a pain in the arse if you want to take mudguards on and off over the course of the year.