Attached is a scan of a handwritten record from 1994 showing yoke-to-upper-structure gap measurements from 1994, both L and R sides, with tank under vacuum and vented.

The measurements appear to be made with a 0.25" shim and 0.01" pieces of shim stock as they are only in increments of 10 thou.

The 1994 gap appears to vary from 0.25" to 0.33" (80 thou max variation) under vacuum, and from 0.29" to 0.33" vented (40 thou max variation).

Our 2013 measurements, made with a 0.25" piece of stock and a feeler gauge, varied from 0.265" at Station 1 to 0.445" at Station 11, (180 thou max variation, see Jan 28 e-log).

I have not yet found any other records of this measurement but I will keep searching.  The gaps may have varied by as much as 180 thou for many years.

I recommend checking the clearance at all stations and jogging individual stations such that the gaps are within a 40 thou band prior to the next lift.