Servo test, engine off, pump the brake pedal a few times, then start the engine with your foot on the brake pedal. You will feel the pedal go down if the servo is working. You need the whole system assembled and bled up before doing this.
Original brake servo on mine was a Clayton Dewandre inline unit. I don't think Clayton Dewandre are around now, but you might be able to get a seal kit.
Carb, I think, would originally have been a Solex, although not certain, someone else may remember.
Clutch, the clutch itself may be fine, it could be the hydraulics are shot, or the slave pushrod may have gone through the arm.
If that was mine, I would be looking to restore it as much as possible to original condition. Bodges are OK for testing, but in good original condition one of those is probably worth about 20 grand now, and a fantastic thing to own and drive as well.