Some disc braked R4's still have the front bulkhead umbrella handle handbrake, mine does, but it does operate on the rear drum brakes so no need go to floor mounted handbrake. However if your handbrake is on the front wheels I think you will late rear brakes as well.You'll need to check out your current handbrake arrangements. Drum-braked R4s have the handbrake operating within the front hubs, those with disc brakes have an entirely different central floor-mounted handbrake operating the rear hubs. More complications and expense!