In the course of swapping the alternator, I noticed that the bolt that holds the adjustment bracket arm onto the front (the part that faces in the direction of travel for the car) of the timing chain cover was loose and on its way to falling out - which could have been a bit of an issue as I assume it would have happened on the motorway, at night, and in the freezing rain.
Yes, it's my fault for not tightening it up the last time I adjusted the fan belt, but the whole adjustment assemblage is a pain - I begin to regret undoing the imaginative work that the guy who swapped the engine from the TR7 Sprint that dissolved did to fit its alternator in the Sprint engine bay. That's because the TR7 uses the other hang/hand alternator to the Dolomite, and so has the adjustment at the top, not underneath the alternator. Anyway, it is what it is.
I was thinking that I could fit a 5/16 UNF - 5/16 UNF stud into the block and put a thin nut on first to hold the chan cover. Then hold the adjustment arm with a nylok nut, so it could be loose enough to move when adjusting the alternator without undoing that bolt. However, I've had a better idea, which is to get a spare adjustment bracket arm (thank you Alun), drill that out to 11 mm, and use two T washers. The bolt will then clamp the two washers together to hold the chain cover, with the arm able to swing on it without undoing the bolt.
Graham