I've got to say I really liked your original setup with the modified bush.

I had ordered anRNA4907 bearing which arrived today, the OD is bigger than yours but the 20mm width is the same. For the oil groove to align with original I'm thinking of making a 4mm ring to sit on the inner side of the crank, then maybe a thrust washer inboard of that.

[Linked Image]

How will you hold your aluminium plate in place?