Bigwan

I did, NOS off ebay for SIGNIFICANTLY less than half the rrp. While it's fine as a fancy bluetooth speaker (with an unimpressive range!), it farts at any volume with a bass. There have been a few suggestions on mods to try and fix that but not got around to it yet. Scared what I'll find when I do... It pains me to say it but I tend to agree on all points... 3 of the best bits of bass gear I've ever owned have come from the Ashdown fold (ABM 1x10 combo, LB30, J-Lo Hyperdrive)... but with a disproportionately high number of new releases there seems to be some proper whacky decision making going on, quite often with pricing as seen here...

I really fancy an Attitude...

ACG. You can thank me later.

Keep the gain low and they are!

Clean(ish), warm, bit of grit - Orange!

Putting the Positive Grid amp aside for a minute, how many sounds do you need? A quick google search says these are £650 - £700. That's 2 used Orange Terror Bass heads, which would be my choice in your position. Need a different sound? Buy a suitable preamp/pedal. Just my tuppence worth (and I'm a PG fan - have the ipad fully stocked with PG plugins and expansions).

I used to, and have another kit waiting to be built (which I'll probably sell on now I have a Helix). It's good, but not good enough for me to pay Darkglass prices. I prefer the Hartke to any Darkglass pedal I've owned.

Series and parallel. These cabs can be 4 or 8 ohm loads each. Run each cab at 4 ohms, a pair in series then parallel with the other pair in series. 4 ohm load total.

Are you allowed to cheat and modify the neck? My initial thought would be to glue more meat around the bass side of the butt end of the neck to get you closer to the bolt on arrangement of your first picture. Don't know what that would do to your truss rod operation though.... Although looking at the ACG pic above you could get to that and make your job easier in the long run...

A Hartke Bass Attack if you can find one used. They're quite awesome. I have both the Hartke and the BDI21 and like them both, but if I had to choose it'd be the Hartke every time.

A p bass with flats and a p bass with rounds. Maximum flexibility.

Mechanical joint is a good idea. It's what I do, just always seemed like common sense, but that doesn't mean it's right. It can be hard to keep things neat though. I always solder on the other side of the board, unless soldering surface mount components of course!

If there's demand you could see a DI version added down the line...

The sleeve of the mono plug of your guitar lead shorts the negative side of the battery to the circuit. So the pedal doesn't use up your battery when it's not plugged in!

I wouldn't if I were you! None of the other pedals Tech21 do in portrait form factor do, and the prymaxe ad doesn't make any mention of it.

With all the knobs up full you say... Good luck finding a drive pedal that doesn't buzz/hum/spit/try to scratch your eyes out when used this way...

Surely I'm not the only person who's seen this... https://www.prymaxe.com/products/tech-21-geddy-lee-signature-sansamp-yyz-bass-pre-amp

Unless you've fitted it to the main pcb your current limiting resistor (clr) for your LED is missing. It won't work without it. Retouching a few of your solder joints may sort out your intermittent sound... And you should always check your build BEFORE you house it in the enclosure. Saves time in the long run!

Didn't the HMT have a hockey stick headstock?

Pa ha ha ha ha ha ha, haha haha haha haha, hehe, haha ha ha... Haha... Ha... Ha... No, but seriously Ashdown, what's the real price?

While that Lehle sounds nice, I'm not hearing anything I couldn't do with my Hartke Bass Attack and hand position/pickup pan.

Well if we're going down the line of chemical burns... Silver nitrate to the nethers when you've infected vasectomy wounds is right up there! Edit: I took it too far, didn't I? I could hear the virtual sharp intake of breath from you all....

Ouch! Never had a nail, but did have a nasty thorn incident... Slightly off this off topic discussion (sorry OP!) I also once stood on the blunt end of a darning needle my mother had dropped on the carpet and assumed it would "turn up"... Which it did, and embedded a full 1/2" into the bottom of my right foot...