Yes. I really like natural basses, but would have preferred a slightly lighter stain. The Player is MIM as is the JMJ. The neck was a tight fit. Lightly finish sanded the pocket only and KYed it in.
I never had a Mustang PJ neck, but I believe they are 1.5".
I'm a P-player and prefer the 1.625 of the JMJ. And I don't love pau ferro. I think my combination is very traditional Fender, if not traditional Mustang. And I like the HB10 lollypops.
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Yes, natural is where it's at.
2nd choice for me is transparent red/orange.
OK, so it sounds like the fit was within normal tolerances, and given that both parts are MIM, one would hope so.
I too think that the neck from your PJ body would have a 1.5" nut width, and current similar models say that they do.
And coming from a 1974 Ric 4001 [1.6875" at the nut, like 50s and some 60s P basses], my main bass since new until about 5 years ago, I also like wider nut widths, but it seems that in Mustangs, those are only found on either the originals from the 60s thru the 80s, or if among current production, only on the on the American Performer, JMJ, or Vintera models [their 3 priciest].
Pau Ferro I have never owned, unless I bought something used recently, and am not yet aware of it having that wood in the fretboard.
And BTW, that IS possible, GAS being what it is.
I would consider a JMJ Mustang, but I dislike the relic'd finish, and I just learned that the American Performer apparently has pickups wired like a Jazz, where if you only use one at a time, you can get hum.
So my only choice among those 3 might be a Vintera, or a used original, or look for parts like you did.
How did you luck into not having to buy two whole basses ?
Did you purchase a complete JMJ to get the neck ?
It's stupid that they do not offer a Mustang in the Squier Classic Vibe series with the 1.625" nut width of the originals, regardless of the electronics which it could also contain.
And while they're at it, do a Maple fretboard option.
Fender is overlooking a market segment/opportunity, and if they addressed it, would save a bunch of us from doing what you had to do.
There, I got my rant in as well.
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Tried a Seymour Duncan SJB-1 Vintage Jazz in the bridge, then a Duncan SJB-2 Hot Jazz in there now. Might be the Chromes, but neither does it for me. Nordstrand Split hum cancelling in a box next to me. We'll see. 
