Originally Posted by A-RASSS

Sure, but you HAVE to use a R03 underhead.

The kit of R03 internals come (at least here in Spain) with piston , sleeve, conrod, underhead and shims (0.6mm).

If you buy the kit just install it all, if you only have piston sleeve conrod of R03 you must buy also the underhead.

I dont know which air reducer you use in your JPWC, stock came with 9 mm (black). With R03 internals probably you'll need to switch to 8.5 mm reducer (blue).

Where to buy them in the states i dont know, but in any shop which sell JP products they must have spares, try broocklyn, give a call to ritchie, or maybe in fastnfuriousrc.

Best regards.