
Posted on Nov 11 2023 04:58 AM
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You got a new car! Nice! I have to say, this isn't technically a Jagmaster - the Vista series and the later Vintage Modified are a Jaguar neck on a Jazzmaster body, which is where the name comes from. This is a Jazzmaster neck on a Jazzmaster body... it's essentially the same as the recent Affinity Jazzmaster, just with humbuckers.

As you might imagine, I do not see this as a detriment. Here's my two - and apologies if you've read the histories of these before. Lefty there is almost stock. The nut is different, the trem block and arm have been replaced (something I STRONGLY recommend, if you can find someone who'll machine you new ones) - and finally, it recently got a Switchcraft jack because I was replacing some badly done wiring, and I didn't want to re-solder again to such an old, cheap jack. I love it - and the replacement block actually cleaned up the muddiness of the stock humbuckers, something unexpected but not unwelcome. Honestly, the pot metal blocks are trash - they don't hold the arm well, and they are a genuine tone suck - something I didn't believe in before this swap. I also spent the last 10 years thinking I'd had CTS pots and a dropcap put in - nope, all stock from 2003. So, no need to replace any of that unless it's actually broken (and not just dirty).
As for moddy on the right - nut, block and arm again - this one was a donor for the left one after some broken tuners, so has Sperzel's. They've actually needed a lot more maintenance than the Squier ones - other than my accidentally shattering a few of the latter - I used to be a lot rougher on my guitars. Again, unless yours are actually broken and you can't get more of the Squiers, there's no reason to change them.
Here's what it used to look like:

The P-Rails certainly made a good job of giving "standard single coil" and "fat single coil" in the bridge, and by middle-position-ing it with the neck humbucker (actually the stock bridge humbucker) I was able to get some great emulations of neck single coils by using the push-pull switches to turn the bridge coils off independently. Now, I'm designing my own pickups for it (the empty bobbins you see in the first photo) to try and get a sound closer to a Jazzmaster - because you can't put real JM pickups in without removing wood. Hasn't stopped a couple people here doing it, but it's not something I was willing to do on an almost-vintage guitar (5 years to go!) I've owned for 15 years. 
I've also seen a three-single load-out like a Harley Benton, but on this guitar with a Strat neck and a Strat bridge - you'd just have a strat. The Mustang set-up has also been done (in that SG101 link above) which is a bit more interesting. And I've seen things like P94's and Gold Foils a number of times on other sites.
I still really like the P-Rails as a solution for the Jagmaster - and I really found that the rails+humbucker gave me plenty of versatility - "P90" plus neck gave a great stratty neck sound, "Strat Rail" plus neck gave a great P90 sound due to the way the phasing worked. The only reason I pulled it was because the pickguard was shot and I wanted to try something new. To be honest - a pair of white P-Rails is kind of my fallback if the DIY pickups don't work out.
Well, regardless - it's a great, great guitar and it'll sound amazing. But I really do recommend trying to get a replacement block for the bridge. I can put you in touch with a guy, but he's in Wales UK - so that might cause you some issues. 
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- "The Mysterious" Tqi.