I am updating this thread with my solution, in case others want to copy.
I ordered (2) 60 lb gas springs from McMaster Carr (about $17 each). We fabricated some 1/8" steel brackets to sandwich the fiberglass under the rear bodywork.
The gas springs come with 5/8"-16 ball stud ends. For the lower mount, we measured 8.5" from the rear subframe crossmember (this is mentioned in one of the other threads as the Olthoff way of doing it). We drilled and installed 5/8"-16 rivet nuts into the subframe at the measured location.
The upper mounting point was an educated guess from the Olthoff photo and other references. Note that we drilled three different upper mounting points to be able to adjust the geometry and overall action of the installed springs.
I may replace the 60 lb units with units having a bit more force. But the action is very smooth and I believe better than a single spring could be.
Cheers.