Powder coating on a bearing surface is a big no no.
It's going to turn to putty quite quickly as the arm moves in service.
(Obviously with hindsight) the surfaces should have been masked before coating.
Unfortunately those faces will have been grit blasted at best and at worst could have been power sanded.
You'll have to see if it's saveable by removing the coating, checking the faces for flat and square with the pin, then start from scratch with the shims.
I couldn't comment on the pin length, but I do know that single siders use a different length.
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