While removing Scarlet's (1959 Bugeye Sprite) steering rack, in preparation for painting the engine and engine bay, I noticed a 3" x 1" metal shim had fallen to the frame as I unbolted the passenger site of the steering rack. I then checked the driver's side (left) to see if there was a similar shim where the pinion gear was mounted. Not seeing one, I headed to the internet for answers!
The piece in question is part number 46 in the AH Spares exploded parts image. Moss Europe lists the shim as "SHIM, packing (nearside)" -- nearside being defined as "the side of a road vehicle closest to the curb." i.e. the passenger side.
A closer look at the pinion we find that it is not mounted at a 90 degree angle to the rack. Apparently, the designers of the Bugeye at Healey took a standard off-the-shelf Morris Minor steering rack assembly for use in left hand drive Sprites. When they got ready to bolt the rack to their newly designed chassis they found they needed a "packing" shim on the passenger side to make things line up without binding.
There are three different thicknesses listed in the Factory BMC parts catalog: 3/32, 5/32 and 7/32. I would guess only one needed but it's listed as A/R (as required). I took some measurements of my packing shim and found it to be 3"L x 1"H x 5/32" thick.
3"L x 1"H x 5/32" thick packing shim