No, I got rid of the old MC after measuring the rod to clevis setting which I copied for the new MC. I've got lots of thick insulation besides carpeting in my car so maybe thats the problem, but in the SM they makes it sound like the 8 7/8th is the distance from the toe*board metal pedal stop.  May be I'm reading it wrong and it should be from the thin OEM carpeting.

Haynes Repair Manual says the measurement is from the upper surface of the pedal pad to the metal surface of the toe board.

That  being the case, with my stopper backed all the way off, mine is only at 8". I can't see how I could get it to another 7/8th inch.

 Interesting. The adjust is 8" on the 240's. A stretch of the imagination but is it possible you have a 240 pedal box in your 280? It could be, if your Z was originally an automatic. The problem did exist when you bought it. If that's true, I think you would need a 240 master cylinder.  Anyone know what the difference in the pedal box and clutch cylinders from 240 to 280?