i made a set from 1/4" plate aluminum. Not sure of the aluminum type. Not sure if it really matters that much. I don't remember the hole diameter I just matched existing using drill bits to fit through the old hole.

I did have a conflict with the swingarm and the pipes. Ended up going back to stock suspension. Would like to hear how you overcome that problem.
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MC21R9N track
MC18R2J track
CBR954
CR250