I played with the old clutch from my MGB. I could only activate the pressure plate "manually" by bouncing on it as if it were a springboard. I weigh about 190lbs... If you think about the pressure one normally applies to the pedal, and multiply that by the mechanical advantages of the pedal arm, Hydraulic system and release arm combined, you can get a feel for the amount of force involved.
The advice to replace the whole set is very wise.
Cheers,
Ed
I want my MGB