I agree with Jeff. That's a lot of stress being applies to a small bracket attached to fiberglass. Napa has struts that will hold the weight for under $25 each. You can prolly get the mounting hardware at Grainger Supply.I would think it would be easier to fabricate a strut system rather than use those springs.
Donny some close ups will do.. Thanks.....Heres mine on the 68
I can get close ups tomorrow if you want
And really no stress on the cover. I can open and close it with 2 fingers, (you figure out which ones!!!:nanawrench