I tend to agree Andy, in the day Honda will have spent many engineering hours perfecting the design of NSR parts + then employing top manufacturing quality.

I'm going to whip the barrels off my 21R trackbike, if the 'L' barrels are OK, I'll probably go with SP 'L' heads to reduce the squish. Forking out for another 2 sets of barrels (R 'H'), just after my 21SP rebuild is some step

I should have snapped up Dan's 2nd hand SP heads for sale at £30

If nothing else, at least I've got my head around the barrel / head combinations now. Thanks to you & Steve for the info.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30