It has been done. I dropped Brown off at Brian's yesterday and when I came back this afternoon I was pleasantly surprised to find out that he'd almost finished. I'd expected him to be part way through the job so I helped him to finish off. There was just the radiator hoses to fit, the cooling system to fill with fresh coolant (I had plenty of antifreeze) and the bonnet to fit. He wasn't able to flush the cooling system properly and replace the themostat because one of the bolts for the thermostat housing wouldn't budge and he was loath to try to undo it for fear of shearing the bolt head. When it came to starting up the starter motor wouldn't spin. My previous bypassing of the inhibitor switch got the starter turning again and we ended up carrying over the inhibitor switch and wiring to the multiplug connector from the other automatic both of which were tested beforehand. Apart from adjusting the transmission lever there weren't any other problems. As suspected the auto box that was in the car was a Borg Warner 35 so Brown now has the correct automatic. (Borg Warner 65) The BW35s were used in the Triumph Stag so I suspect that a previous owner was only able to get a BW35 and was told it would fit as they're virtually identical. I want to put plenty of miles on to make sure it is fine and so far it is leak free. I'll be changing the transmisson fluid in the next couple of days. My other suspicion about the source of the leak was confirmed by Brian but it wasn't the torque converter. He said that it was the front seal because he said the torque converter was covered in fluid when he removed it so it'll be a fairly simple repair. I'll try to sell it on as it is the wrong auto box for Brown. Maybe one of my Stag owning friends might be interested as it is in working order.
Brian thanks a million. You're an absolute star!