Steve... See if there is any appreciable distance between the stand pivot and the spring mount on the stand when the stand is either raised or in the lowered position, you need to be able to stretch the spring the least distance.
Then its a case of hooks, levers and bars to get the spring eye into place.
Far easier to make the stand the first job of any rebuild... Plunger Stands wear their top ears and also the flat area of the frame lug where the ears settle with the stand down, resulting in the bike lowering itself slightly as the stand comes to a stop. Then you have to lift the bike to get it off the stand. An unworn stand and a nice undamaged area for the stand to come to a stop makes getting on and off the stand a whole lot less physical.
With the bare frame upside down, easy to fit the spring, put a thin bar through one stand pivot hole and use the leverage afforded by the stand to line up the holes and insert the first pivot, then the second.
Bit late now but if someone can hold the bike while you unbolt the pivots, you could try that.
Swarfy.