That discussion reminded me that there was also an issue with using the Dolomite Sprint pully on one of the fake the TR7 Sprints, that the pullies on the TR7 fan boss and otherwayup alternator mounting didn't line up well and it ate belts.
So I was wrong, and it's not just the timing quadrant that corrects.
I don't understand about the Sprint pulley issue, could you explain further please Graham?
As I said and you've confirmed, the timing marks on the Sprint and TR7 pullies are in different positions relative to the woodruff keyway, i.e. rotated round by different amounts relative to TDC #1. So, if you use the TR7 pully with the timing quadrant (the sawtooth thingy fixed to the chain cover) from the Dolomite Sprint and do the ignition timing, it will be well out. The same is true with the Dolomite Sprint pully and the TR7 timing quadrant - though the timing error will be the other way around.
But, as both you and Alun pointed out, the lengths of the pully shanks are also different. And, from what's been written here and as I remember, you can fit the TR7 pully on the Sprint engine (with the TR7 quadrant), that upsets the alignment with the fan and alternator pullies. So, if that's true, it will eat fan belts. I'm not so certain you can use a Sprint pully on the TR7 and get a seal, but if you can, I think that may eat belts too.
The TR7 Sprint is special, because it takes the TR7 fan and alternator and mountings, but the Dolomite Sprint chain cover. So, as the different chain covers do not move the fan and alternator pullies relative to the end of the crank, if the different crank pullies do move wheel forward and back relative to the end of the crank, it will need the TR7 pully and so the TR7 timing quadrant on the front of the chain cover.
I don't know anything about the 1850. So what's what there is a mystery to me.