Another way to make the adjustment is to just barely loosen the locknut, then unscrew the pushrod from the clevis until all the free play is gone. Then turn the nut so there is 0.1" between it and the clevis. Turn the pushrod back in until the nut touches the clevis, tighten it and you're done.
Either way, it pays to double-check that the slave piston is bottomed in it's bore. Sometimes the spring gets too weak to pull it back all the way (in which case the spring should be replaced). Along the same lines, that is a very strong spring. A cut-down screen door spring is NOT going to work!
The only critical part IMO is that there be some free play; the 0.1" is just so it doesn't need to be adjusted very often. It will still work fine with only .010", but the engagement point at the pedal will be a lot higher. Sometimes that's a good thing
Also worth noting that the earlier Lockheed system (on TR2-3 with front drum brakes) specified less clearance. The owner's manual in the Bentley gives .075" while the workshop manual gives .079".
PS, IMO the important part is to choose the hole that lines the pushrod up best with the slave cylinder. On my cars, that has been the bottom hole as shown in the photo that Moses linked to above. (Which is from the factory owner's manual.)