[SS Engine Guy]

Also it is good that the total length of the push rod and lifter to be checked are taken into consideration as Travis noted. If not, there is no assurance that the "checking" lifter seat profile and the push rod end profile from the engine fit together at the same height. The checking lifter seat I use is machined to form a conical "V"shape with a large enough radius that the pushrod cannot be deflected up through out its range of motion.

Another variable is the flatness or how parallel the retainer is around its diameter. For example: Spin the retainer around and check lift at several places and you will get different readings on some depending on the accuracy of the machining. In extreme examples, where the spring winding ends will slightly cant the retainer in that spot.

As others have stated, minus .010 lift won't affect much, however, +001 will ruin your day. So plan on cutting it as close to possible to the edge but keep it within the limits regardless of the circumstances.