The MC on my 53 F100 is also under the floor. Although not power boosted, I bled it successfully with a "one man bleeder" that uses one clear plastic tube to the fluid cylinder and one in a jar with enough fluid in it to cover the end of the tube. You then just start at the farthest wheel, pump the pedal up, open the valve and let fluid out untill no bubbles, close valve and go to next farthest cyl. I believe it took two trips around, but worked well.