The 4th generation watch is based upon a very specific case; the easiest way to identify are 1) The position of the He Valve (slightly above 10:00, as per the genuine) and 2) The coin edged bezel. This is the only model that I've found that will easily accept genuine parts as the dimensions and size are on par with it's genuine counterpart. In dluddy's particular instance however, the genuine bezel would not fit as a 1:1 replacement, thus requiring slight machining to faciltate fit; on my case, the complete bezel assembly was a direct swap and snapped on without any additional work required.
Here is what a later 4th gen looks like out of the box:
Note the location of the He Valve along with the shape of the bezel edge.
After modification:
The 42mm PO from Narikaa is a slight bit different; the diameter of the crystal, bezel and dial are all a bit larger than gen, and therefore those parts will not be a direct exchange.
Regarding the crown; I believe that this is the one item that is not a 1:1 swap with any of the models as the tube is slightly too small for the case. Most people epoxy their crown tubes in, and some have gone so far as to laser weld it in. I myself have been looking for a solution that requires neither glue nor weld, but rather a metal sleeve to allow for a press fit. I haven't gotten around to it just yet, however...