Basically if you can live with the lack of rattle (from the clutch) and the engines are in good condition you won't be able to tell a difference at all.

Anyway I think I'd strip the other motor and swap the gearbox/clutch (not a big job) and keep the spare barrels head and crank for a rainy day before I swapped a whole motor I'd never started for another I knew worked fine.

The R barrels are shorter, the R heads have a similarly larger volume, effectively when the motor is built the head gasket on the R motor it located 0.2mm lower.
In theory the dry clutch should give more power, but it's not a measurable amount.
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