I have not worked on a twin with a bush for many years. When I last worked on my A10 the main bearing bush was a steel housing with a steel backed bush of similar composition to a big end shell. Putting a reamer anywhere near it would have ruined it.
My Aprilia has plain bush main bearings, these are split shells like big ends pressed into the crankcases
Has the idea of reaming come from after market solid bronze bushes?
The original A10 bushes were steel housing filled with white metal ... you are dead right ( as i tried to explain earlier) a reamer would tear super soft material like that to bits The Original A65 bushes were steel with some mystery liner with a very thing copper colored coating. a reamer would also be the wrong tool
reamers are only ok for comparatively hard materials like bronze in bushes .