I could use a refresher class on the MK1 and 2 AC alternator setups.
The long curved bracket might be for the AC alternator.
It mounts on top and that bracket goes to the head.
I think that's how the belt was tensioned.
The factory MK1 AC bracket had that small alternator mounting hole, that is threaded like you mentioned.
And it has that lip right below the alternator pivot bolt that keeps the alternator from being rotated downward.
The MK2 alternator can be rotated down in a MK2 bracket, with a little grinding, for an AC delete.
All my rabbits have the MK2 90 amp alternator/bracket upgrade.