1) if set up with a mic, will they (adj. reamers) hold true when used for fairly precision jobs like the timing side bush?
No, adjustable reamers tend to cut tapered holes and with what in the UK is called threepenny holes, ie like a hexagon.
Send your cases to someone who knows what they are doing.
Such as Site Sponsor EdV
https://www.shopevengineering.com/
or 
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