Hi Apache59 . . .
I was mistaken. I been down this road but not on this car.
I just looked at my car and the Fisher body manual. This a compression setup - not a tension set up - so that over extension technique I described doesn't apply.
With thunk lid raised to its highest point, the spring assembly should neither push or pull on that back pin. The service manual doesn't mention a need to compress the spring to install.
In looking at my car this morning over coffee it seems that the weight of the lid just starts to compress the spring (with the lid open at rest). And if you pull up on the lid the length of the spring assembly acts like a check link - preventing you from raising it to high. In between these two positions there doesn't seem to be any load on that back pin.
The old car manual project has the Fisher Body manual for 49 online:
Page 47 Page 91 Page 92 regards,
stock49