You guys might be on to something with the colour of the gears: black - spiral goes one way, white - the spiral goes the other. That would certainly be a sensible way to do it if you had bags and bags of near-identical cogs at a bike factory. Certainly the "correct" one I have on order is white.

I have the original '70s Haynes manual (Euro equivalent of Clymer although not as good.) It's a little confusing as it covers all the European DTs from 1971 to 1985, 100/125/175. But 100% definitely the wiring for the DT175 1G1 is different to the DT175C which I surmise is the closest US cousin - the Haynes manual has the only correct wiring diagram for my bike I've seen so far.

The spare bottom end I have is marked "1G0" which tallies with Haynes. I've only had a cursory glance at it as it's been coated with oil and wrapped in plastic to aid preservation. It's much larger than the 175 bottom end which I'd expect given the magneto doubles as a motor. Hang on...

Okay, so I've had a quick peek. The magneto side is much, much wider. I think the clutch arm is missing so no comment on that. Speaking of missing....

Aha! The tacho drive is completely absent. I think we have a high certainty of where my parts came from Mystery solved?

Another one for the "What a Previous Owner Did" reference library!

A US member of the aircooledrd forum has just found a slider from a different bike in one of his DS7 carbs.

The US import RD350B that I bought off fleabay (I know, stupid me, but I never learn! ) had carbs from two different bikes fitted - one off a RD350LC and one off a YR5. And neither of them complete. Basically just space fillers for the photos. At least I could sell them for half decent money.

Oh, and just a taste of what I'm working towards:

Very nice look... don't see too many in black..

Yes, Europe had different lighting requirements in the later years so the wiring is slightly different. Mostly changes are a "city light" or "parking light" in the headlight if I remember correctly... I think there might be an extra key position for that too.

It would be interesting to see the ads you found with reverse tach gears... I have the parts list for the 1GO and it takes the same gear that most did... the one RT325 posted, so even though tach gears are missing, it's not likely they came from a 1GO.

(Clutch actuator is mounted in the chain cover which is probably why you didn't see it... you'd have to remove the cover... if cover is gone, so is actuator... all you'll see is a pushrod in front of the sprocket.)

Oh, and as far as it being black instead of white, the part number has an "02" which means a revision... could be why it's black plastic now.