I'm likely the worst person to ask on this as I tend to follow the "use new parts, but build it like it has 100K+ miles on it rule."
Case in point:
2 seasons ago I took an iron 5.3 truck block and filled the water jacket with concrete. We punched it +.03", gapped the rings like a pair of 8-year front teeth, and set the mains up with .004" and the thrust with .0045'. Rod bearings were around .0029" if I recall. (don't quote me on that as the mains were the big deal) I ran 5-40 Rotella through that thing on a HV/HP Melling pump. We had 65 psi all the way down the track and when I pulled caps mid-season, there was almost no evidence of anything. One or two little smears here and there. The thrust bearing had nothing other than a scratch from some dirt.
This was a 10.5:1 CR motor on methanol with 35psi worth of 8.3L Whipple blower plopped on it. The guess on power was somewhere in the 1100 zone. We spun that thing up to 7500 on a .670" lift hydraulic roller camshaft. -Morel High RPM hydraulic lifters.
As for imperial to metric conversions and bearings. A tenth by itself likely won't hurt a thing. Just be sure your rounding to a tenth and not a thousandths. (.0001" vs .001")
On another note for anyone running boost and methanol. Something I recently ran accross that makes a great deal of sense to me. (like DUH! sense):
Gap your top ring as called by the setup. (ring material, piston material, bore size, distance from the crown, fuel, boost, nitrous, whatever...)
Gap your #2 Compression ring fatter than the top as called by the setup. (see above)
Gap your TOP OIL RING the same as you do the #2 compression! (Meh?!)
Lots of sneeze (boost) and methanol translates into a metric piss ton of blowby. It's going to happen. The trick then becomes venting off that pressure from between the #1 and #2 compression rings. Gapping the top oil ring all fatty like allows that pressure to piss its way through the oil return holes poked into the oil ring holes of the piston. The poison to avoid here is lifting a compression ring off of its seat when under load (power/pressure) as this is how ring flutter starts and that kills the seal and beats the snot out of the piston and the bore.
Good luck. Eat well tomorrow gents.