I kind of guessed it might be the later 1M100 which was the "monoshock" engine.

I don't know enough to say the smaller reed was a "downgrade" or it was done to better match the desired character of the engine? (Throttle response, etc)

The 43800 is the original type.

Pretty sure that the pipe in your reference photo is from circle f. If you want the bike to rip you should consider adding it to your list. Bike is from @onedownfourup if you are looking for more pictures.

Will be considering a pipe for the DT, The circle F looks very sweet!

New points arrived, found locally for $20 delivered. The old points look knackered. Hopefully this will sort the spark out.
Also have freshly bored cylinder, new piston and rings too. I should be able to start assembling later this week

Does anyone have any experience with front end swaps for the DT?
I am looking for a disc brake front end preferably adjustable for compression and rebound.
I have been looking at late '80's early 90's kawasaki KDX 200 as a donor. They have a conventional fork, disk brake and will fit the DT head stem bearings. They are also widely available and cheap.
Anyone else done a swap to disc brake? What did you use?

Have a look at early RT 180 pre 91 should be very close if not a direct fit.Not too sure they adjust though Race Tech’s latest vintage model fork kit fits vintage Yamahas with 34mm KYB forks.

Biggest potential problem is most (or maybe all?) off road/dual purpose bikes went to "leading axle" forks before they went to front disc brakes.

Trying to use the leading axle fork setup on a bike that had standard axle in line with fork tube like the 74 DT will almost certainly result in forks and/or triple clamps that will hit gas tank at full lock... and you don't want to use leading axle forks in triple clamps designed for standard axle forks as that would reduce trail and could result in a dangerously unstable bike.

I've seen people use forks and triples from something like an RD350 but usually on a "street tracker" type build... RD350 front end is heavy and brake is way overkill for an enduro.

Thanks, will check that out. I am not familiar with RT's, looks like a dt175 though. Maybe that's how they were sold in Australia.

Thanks Mark, I will definitely consider this. I plan to make this bike a street tracker for on road use only. If I could find anything for an RD in Australia for a reasonable price I would consider it.
Out to the garage to study the triples and steering on my other more modern bikes!

I once converted a it490 to disc brake by building clamps around the fork leg, it worked, but dont know if it was worth it ( those IT twin leading shoe brakes are pretty good) ( theres a thought for you) also seen people weld caliper mounting lugs onto the fork leg. But I've looked at my Enduros fork leg and thought that the mudgaurd mount looks like a good place to mount a bracket that ran down and picked up on the axle as a wheel spacer and then the caliper could pick up off that. Being a street tracker it would have to be all done in polished alloy of course.... and speed holes !