Master Cylinder Bellows

I wouldn't trust that tear drop to hold the piston in place. Think about what would happen if you accidentally pull up on the brake pedal (my shoe laces have gotten wrapped around the pedal many times over the years). My bellows plate was also all bent up from master cylinder removal (pulling pedal back to remove rod from master) over the years causing various issues (pedal not returning properly causing lights to stay on, dragging brakes, etc). I made a new plate using the bellows plate as a template for the piston stop. Just make one picking up the two tapped holes clearing the firewall when you reinstall. Wouldn't be too worried about the missing boot.