For what its worth we installed a Honeywell "LaserNav" system in our 737s a few years ago. The rack wasn't a big problem as long as it went in exactly as per the drawings but we had a set of complex alignment procedures to do with assistance from Honeywell engineers. Memory is a bit hazy now but as far as I remember, this involved lining up the aircraft on an accurate heading using brass studs set into the hangar floor. Surveyors (the kind with theodolites, not the CAA variety!) had first surveyed and marked an accurate line and installed the studs. We then lined the aircraft up on the studs. The checks assessed the alignment of the gyros by comparing the earth rate figures obtained from the gyros to the calculated rates based on the accurately known aircraft alignment.
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Through difficulties to the cinema