I ordered a 100 amp alternator to replace the 65 amp which came with the car.
It was working but occasionally it seemed the battery wasn't getting full charge,
possibly due to the rear location and long cabling. I also have no idea how old
it was, so seeking something new.
The new one is for an Astra Mk2/Astra-van supplied by parts_eu via ebay.
https://www.ebay.co.uk/itm/187656030152 It's Chinese, but appears good quality.
This unit has 10mm bore lower flanges, the rear being a slide fit. I used a couple of M8 steel
riv-nuts, turned down to 10mm o/d and drilled 8mm.
A test fit showed that it would be ok, however I found that the pulley wasn't
quite in line and that the belt would slightly foul the power steering belt.
I didn't want to alter either the alternator or the mount so I removed
the pulley and turned down the rear boss by 4mm. Another test fit and all's good.
The belt would work if I modified the top adjuster bracket but I didn't want to do that
either, so a new belt should arrive tomorrow that is 15mm shorter. An estimate but
I can return and reorder if wrong!
The orange bush in the adjuster arm had collapsed so I found a plastic spacer from
a TV wall-mounting kit which pressed in with the vice, perfect.
I had to rework the electrical end fittings to fit the 8mm stud but that was easy.
Now waiting for the belt and final fitting.