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I agree this is a place for a lot of attention that is usually missed and always corrected at the bearing surface.But as Dan clarified take as little as possible from the block bores.Having a cam bearing spin and ruin a bore or come out and catch in the lifter area can be costly.If we don't think the fit feels snug enough we will put sleeve/retainer seal behind the bearing,especially on aluninium blocks. 
as far as i'm concerned, all aluminum blocks get loc-tite on the cam bearings at the very least. on blown alky motors running the larger cam cores i normally pin the cam bearings in place as well since they often see 1400+ pound spring loads on a larger bearing surface that could potentially grab a bearing and spin it. it's just a lttle added insurance.
machine shop owner and engine builder
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