clutch problem in a '57 T-Bird

[dmsfrr]

I recently bought a driveable project '57 with a 3spd OD transmission. I haven't done anything with clutch hardware since the 70's and don't remember as much about it as I'd like.

Some background info (a novel in a three paragraphs)....
The clutch seemed to be working fairly well but the action was all near the top end of the pedal travel. The adjustment nuts on the threaded rod to the throwout lever/arm are approx 1/2 to maybe 3/4 inch from the end.
While beginning to pull away from a stoplight the other day I felt and heard a sound like a big spring popping in the clutch pedal while the car tried to jump the crosswalk. Driving it the last few miles home the clutch still works well but the action is now closer to the floor and the pedal sags instead of coming up the last inch or two of pedal movement.
A '71 stickshift Merc I had back in those days used to break the inner/lower arm of the clutch cross-shaft with a similar result, so I looked at the linkage first and didn't notice anything unusual. There is a large clutch pedal spring under the dash roughly parallel with the steering column, at first glance it seems ok too. (but I could be wrong)

My dilemma: I'd like to drive the car for another month or two if it's an easy fix because the weather here is still nice enough... but the engine and trans will be coming out this winter for some other work and if fixing the clutch will be a bigger project I'll just pull the engine sooner instead of later.

Where and what do I look for next?
.