If you're measuring the depth of the diaphragm spring with the pressure plate off the flywheel, you're guessing in the dark. To get a good comparison, the clutch disc and pressure plate would need to be bolted to the flywheel, and the distance from the transmission mounting face of the bellhousing to the spring fingers would need to be measured for both old and new assemblies. A badly worm clutch facing would make the old assembly measure a little bit shorter than a new one of the same design. If there's a noticeably longer measurement on the new assembly, it would account for the different position of the fork.
Jerry
