I have an M416 with a metal lid from Sierra 4x4. My struts are located as follows:
The attachment to the lid is dead center on each side
The attachment to the tub is 8" from the front edge, opposite from the hinge side.
This picture may help.
Th lid is at least 100 lbs and the RTT is an ARB so it is 100+lbs as well.
I am using two 175 lbs struts .
Hope this helps