Kerry I did it like this. My struts are 20" extended and 12" compressed. So it gave me a 8" stroke.
I measured from A to C 20" 2"below the edge to clear the 1 3/4" thick door and then marked it with a swath of tape inside and out.
I then almost closed the hatch and marked the position of A in the closed position and it gave me B.
Then I made sure that position B and C were 12 1/2" apart adjusting verticaly on the swath of tape. And transfered that to the inside.
I got lucky on the struts. I got 120lbs on each side and they were perfect. I got the struts at NAPA Because they said it would be no problem exchanging the if the pressure didn't work. They had most pressures in stock also.
