I could not find the details for the struts on my 2700 anywhere ( it was missing when i bought the boat ) so I ordered an adjustable 2400N one from here:
1) Measure the distance between the mounting points with the hatch closed. That is the minimum compressed length
2) Measure the distance between the mounting points with the hatch open. That is the maximum extended length.
3) guess about how heavy the hatch is to lift. That will equate to the lbs.
Remember the hatch is only assisting with the lift, you are still lifting the hatch.
More is not better. I installed struts that were to high in poundage. When I tugged on the deck hatch it would fly open too fast. You almost had to be careful not to get hit by the hatch as it sprung up.
If you can read the numbers on the strut, they contain all the info you need to order a gas strut even the pound rating. You can often order a strut with the exact same physical dimensions but with a higher pound lift rating for more assist opening hatch.