Thank you Julian very quick off the mark.
Looking at the pictures it might be doable, the adjuster is at the wrong angle (I think) to work efficiently, but if the alternators are interchangeable (are the mounts the same?) the adjuster on the current one might be utilized in some way. Belts are available in various lengths and if the exact one is not avail you could no doubt use an A/C adjuster as a jockey wheel.
The biggest problem I see is trying to do this in situ you really need an engine on the bench to play with and iron out the problems, sadly as I have neither presently its a non runner for me.
I also just had the thought that although it moves the alternator to a better position it's not really more accessible as you would have to remove the engine cover for service. Easier and more comfortable yes but more accessible probably not.
Thanks that is very interesting a long time ago I found a site that listed belt types and lengths available off the shelf but can't for the life of me remember where. My memory may now be kicking in it might have been a belt manufacture AC Delco or some such amazing what typing it triggers in your memory.
I think it may work directly to the crank pulley (if nothing in the way) my only concern is the belts would be relatively close to each other near the alternator and I have no idea how much they whip or flex in use (if at all). This would also mean not having to source A/C parts which I imagine are maybe scarce and therefore expensive.
This appears all too simple to me but might be worth a look over winter when she just sits there certainly not now with the sun shining.