ikay

I did think of trying a shim on mine when I first got it. I removed the bolts but the neck was such a super tight fit in the pocket I decided to leave well alone. I think the tight fit of the neck is part of what makes it feel and sound so alive. The bridge is also tightly bonded into a recess in the body so energy transfer is maxed at all points.

String heights at 12th fret for my RA Mouse are: G - 7/64" (2.78mm) E - 10/64 (3.97mm) I have mine set up with an almost dead straight neck (just the tiniest clack of relief) so there's no further lowering possible on that front. The stock saddle is already quite low profile with just 4/64 (1.58mm) being above the saddle. You could probably lower this by 1mm max but it may affect string pressure on the piezo. Personally I wouldn't do that as there's really not enough leeway to play with. The Mouse really doesn't allow for a super low set up. On the other hand, the medium/high stock setup is optimised to allow a great dynamic range - and boy this diminutive little beast really does sing! The whole instrument feels alive in your hands, it's like no other bass I've ever played. I actually prefer a medium/low setup on my regular basses, but the higher action on the Mouse doesn't bother me at all. The nylon strings are very compliant and easy to play. The higher action allows them room to vibrate freely which lends an incredibly expressive character to the sound. Couple of pics below

According to this TB thread, a good rule of thumb is to treat the Epi 310 as if it was a 4 ohm cab: - https://www.talkbass.com/threads/epifani-ul2-310-ohms.1313100/ Set your amp to 4 ohms and it will be fine with a cab that's rated at 4 ohms or above (but not below) so will be ok with the epi.

Ibanez PCBE12MH (32") - https://www.pmtonline.co.uk/ibanez-pcbe12mh-opn-acoustic-bass-guitar-natural

Limited Edition I see, hope there are enough to go round!

Yes please!

This pic showing the relative pickup centrelines of the usual suspects may also be useful

I'm a bit OCD about measurements and suchlike and it just so happens I have a spreadsheet of pickup position data (attached for info) Pickup position.xlsx

I had a Squier ebonol fretless with the same issue of the slightly raised fretlines. I gently sanded it using a fairly fine grit until it felt flat to the touch and then polished it up using a series of micro-mesh polishing papers like these - https://www.amazon.co.uk/Micro-Mesh-Regular-Sheets-Abrasive-Polishing-x/dp/B003RTABUK. After the first sanding the surface goes scarily grey/dull but the finishing papers bring it back to a full glossy shine. Or you can leave it somewhere in between by just stopping the polish at a point that you're happy with. I was never happy with the neck though as the ebonol just felt a bit fake compared with real wood and I could always imperceptibly feel the plastic inlays. If you do change the neck I believe that both the Fender MIM and USA fretless necks also use some sort of synthetic material for the fret inlays (not wood) so be worth checking that out first.

I think the problem is to do with the intonation of one or more individual strings. It's easy to move the whole bridge and get the outer G and E in tune, but the little 'fretlet' saddles are set in grooves and don't always have a fine enough back/forward adjustment to intonate the inner strings correctly.

I doubt that you'll find anything off the shelf. One thing you could try is to cut slots into the existing floating bridge and add some simple sliding saddles similar to the pic below. Something like that should be pretty easy to fabricate.

I use D'Addario EXL170M - http://www.daddario.com/DADProductDetail.Page?ActiveID=3769&productid=130&productname=EXL170M_Nickel_Wound_Bass__Light__45_100__Medium_Scale

Taking the vol and tone pots out of the circuit will change the load on the pickups and make them sound quite a bit brighter, even harsh. It will not sound the same as running it with the pots all dimed. You may like it, you may not, depends what sound you're after. Easy thing to try though and easy to reverse.

Here's a thread from TB if you haven't seen it already - https://www.talkbass.com/threads/hofner-icon-dead-replaced-by-the-ignition.615049/

I love my Hofner HCT Club bass. No complaints at all, it's very well put together and sounds great. The staple pickups are amazingly punchy and with Pyramid flats it has 'that' hofner sound. I use it in a little jazz trio and it has just the right tone and vibe for what I need. It won't necessarily work for every band situation though so depends what sort of thing you're after.

Spec for the BJB on Nordstrand website says radius is 14" https://nordstrandaudio.com/collections/4-string-jazz-bass-pickups/products/big-j-blade-4

Threaded barrels alone are available on the G4M website here - https://www.gear4music.com/Guitar-and-Bass/Fender-Vintage-Saddles-for-Bass/1IYJ Not clear if £6 is for just one saddle (ouch) or a set of 4 (bargain)

I think the switch was made somewhere around 1964.

Earth wire from bridge goes to sleeve of the output jack.

This interview with Mike Watt might give you some ideas - http://www.flyguitars.com/interviews/mikewatt3.php

It's a Maruszczyk Frog Omega

Testing in a different room is a good idea. I had a wierd string resonance issue that was eventually tracked down to sympathetic vibrations from a glass cabincet in the corner of the room. Another common culprit for wierd notes is a twisted string (can happen when installing new strings if you're not careful).

Here are the dimensions of the Fralin if that's of any help - https://www.fralinpickups.com/product/jazz-bass/