Here's the parts book amendment advice showing the heater/demister ducting parts numbers for the Cooper S (first used on YG2S4-2808), and different parts for other 1971 Mini models that didn't have a power brake booster in the way, so could use a single wider tube.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Thanks for all the info, I have a pressed pipe like adapter that bolts over the hole in the fire wall from the original deluxe design. My main objective is to get some fresh air flow coming in through the drivers side windscreen vent and add some sort of vent at the rear of the car so the cabin has constant air flow when moving, this I hope will help the car from fogging up on cold winter days as soon as I turn the heater on. Has anyone tried or seen this done before, I have seen one example where a vent was in he back parcel shelve and another in boot lid under the number plate, the owner of the car said it worked really well.

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1968 Morris Mini Deluxe - members gallery
1970 Morris Cooper S - members gallery
Mini's I grew up with
Slot car couch

That looks like an easy and good option

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1968 Morris Mini Deluxe - members gallery
1970 Morris Cooper S - members gallery
Mini's I grew up with
Slot car couch

I have the same 80mm ducting on my 'Matic as Timmy, I bought from Purple Pig.
But I cut it a bit shorter and sat an Attwood 3" bilge blower in the firewall to keep my tootsies warm stopped in traffic.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.