I think if you drill a 2BA hole between the 1/4 and 5/16 holes the FT203 will hold the plate to the FT22as by this method your plate self aligns for the spring angle.
Just to confuse you further, my "H.R.D." Parts list from around October 1947 shows part no. 561 going through from the INSIDE with 142 and 143 nut and washer outside. However, I have an early "B" R.F.M. with a 5/16" B.S.F. bolt going from the OUTSIDE in this locationI am thinking about this No42E mount, based on all I have read (Throwing Light) and using the photo as reference, that the 42E mounts under the RFM leg bolt......which supposedly on an early B Rapide is a 5/16 BSF rather than the later 3/8 BSF. I have not confirmed this BSF personally yet. I flipped the parts manual MO22 drawing to show my thoughts.
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