Bassassin

It's an Aria STB-GT, basically a mashup of a Stingray, a P shape Aerodyne body & a Jazz neck. I managed to blag one for £99 back when it was a current model. I think list was £250-odd back in 2007 or so. The G4M 'version' looks like a steal at £150 - I'm actually relieved there isn't a PJ or JJ version - don't need any more impulse purchases!

That's not a Mats serial or any MIJ that I'm familiar with, and if it's as clearly dateable as it looks, this is post-Matsumoku (the factory closed in 1987) and 99.9% likely to be (as the guy says) a Korean-made Thunder 1A. MIK Westones are pretty uncommon compared to MIJ, & I don't think I've seen a Korean Thunder 1A before.

Where's the groan emoji when you need it?

I'd like to think that saved someone's life in a flood.

Sounds right - DiMarzios are imperial, anything MIJ/MIK & hex-poled will be metric, them's the rules! If you pop it out the wiring should be black/white/red/green - I don't think any Japanese units used that. If you're lucky it might even have PAF stickers...

You wouldn't have what on it?

That's actually pretty cool. I do think I'd have made that centre section broad enough for a proper intonatable bridge, less precarious string retainers & a bridge pickup, though. Wonder why they didn't?

The bendy bridge is another thing that points to Matsumoku - loads of Mats basses from that late 70s/early 80s era had these & they all seem to be made of cheese. This is the one that was on my Westy Track 2 when I got it:

I've never played an SR300, but have owned a few other versions of the Soundgear (there have been dozens - the range goes back to the late 80s!) and they tend to be very good basses, particularly if you get on with a narrow neck. What's interesting about the SRs is that for some reason they've always had a pretty low re-sale value, which means you'll very likely be able to find a used model from higher up the range for the same sort of price as a new SR300.

I've never been entirely sure 'Hondo II' was actually a thing. The logo started appearing on Hondos from the early 70s & I'm inclined to think the part that looks like a Roman numeral is (or at least was originally) just a bit of the design, but it sort of stuck as a name. Later Hondos have a couple of different logos that don't have a number. Aria Pro II was a rebrand/update of the Aria brand, so the Pro II bit was meant to suggest improvement/advancement - although unlike Hondo (a US brand originally owned by International Music Corp) it's proper Japlish & therefore borderline inexplicable. The Aria & APII brands continued side-by-side & have been known to appear on the same instruments, so it's anyone's guess. The parent company is Shiro Arai Co, so at least you can see where it started!

Steal. Probably Matsumoku - my Westbury Track 2 has that style of plate & apparently those were all Mats. Pickup almost certainly a DiMarzio (stick a hex key in a pole piece, should be Imperial so metric won't fit) and worth the price on its own. I love the fact that deals like this still come up.

That's a really interesting read. In its own way, this weird/hideous bass is a proper bit of UK music history, as is its original owner. It should be restored & stuck in an (unfortunately non-existent!) museum!

Conditional recommendation for Streetshirts here - I've used them for band, work & novelty stuff for years. For the most part they're very good considering how inexpensive they are but print durability is variable & I've had a few average-quality prints too. The design interface is OK for upoading completed artwork but it's important to enter the actual size you want the the design to be, not what it looks like on the screen. Not sure how it will handle the OP's (excellent!) artwork but what's good is that a one-off with a single front print is £17 delivered, so not too much of an outlay for a sample. There are significant reductions for bulk & they'll print on any colour shirt.

It's a Musicvox Momo 8-string. Or is it? https://www.ebay.co.uk/itm/305054963788

Back when these came out, I had no idea the Duke existed, never mind that the Alien was a knockoff - I just assumed it was a cheap, low-effort way of making a headless bass. To be fair, I 'borrowed' that concept with my first guitar (originally a Columbus SG copy) after it had a minor accident...

Looks really tidy. If it was local to me, I'd be half-tempted to make a cheeky lowball offer just out of curiosity. Although I did play one of these in a shop when they were new (first headless I ever touched, in fact) and my initial impression was that it was rubbish. IIRC the guy in the shop apologised & said it "wasn't exactly a Steinberger".

Would make several hundred times more sense with proper headless bridge/tuners

That's exactly what it is. Pickup's a DiMarzio Model P.

Looking at the damage, the black's original. I'd put cream covers on it for that pukka 70s look.

Late 70s (hooky headstock shape says 1976 or later), made by Matsumoku. The pickups (or those red covers at least) & the BA2 aren't original, and it may have been refinished - 9 times out of 10 MIJ Jazz copies will be sunburst or natural. For the most part the serials Matsumoku used on 'Steel Adjustable' neckplates are random & can't be dated. They used several different formats but weren't consistently dateable until probably around 1980.