Oops! Should have been posted in the "Replica / Modified Parts Wanted" group. Here goes as we need more info:
How long is your assist strut fully extended?
How long is your assist strut collapsed?
How much pressure does it take to collapse the strut? (Push the one with the most gas in it on top of a bathroom scale)
Take these findings to the McMasters website and match them to their catalogue listings. Be sure to pick the correct ends on the strut also.
https://www.mcmaster.com/#gas-struts/=18xs50w01