The reason the pin breaks is because the hole in the fork is too big. The pin is safety-wired and the threaded part blocks the hole, so there is no way for the broken end to fall out. So it stays in the hole and eventually the the fork twists far enough that the pin jams in the oversize hole. It's not a lot of lost motion (maybe 15 or 20 degrees of rotation), but it's enough to take it beyond the normal range of adjustment.
With the freeplay too large, the return spring pulls the pushrod back against the slave piston, and bottoms it in the bore. (This is normal operation for TR2-TR4.) Pumping up the pedal takes up the excess freeplay, giving you a clutch that works until you release the pedal. Releasing the pedal opens the return valve in the MC, which allows the return spring to pull the piston back and puts you back into the situation where there is too much travel required for one stroke to provide.
I actually got mine to work briefly, by making up a longer pushrod (that could be adjusted with the broken pin). But it fairly quickly damaged the pin and fork enough that I could no longer adjust it.
Getting that broken end out is actually something of a trick; it probably wouldn't fall out even if the threaded part did. The Buckeye article shows essentially the same thing I did: drill a hole through the fork right above the pin, then get the fork and shaft aligned "just so" while tapping the pin out with a punch and hammer.
FWIW, I used an additional bolt to reinforce that joint. 1/4 NF Grade 8, with the hole drilled undersize so the bolt is a light drive fit into the hole. The article presents several other ways to reinforce it. But you still need a new pin to get the alignment between fork and shaft just right.