an easy way to rough set the piston so it cams over is to get a bit of 1/2" dowell or rod and in sert it down the compression tube till it hits the valve
then mark the rod through the lever pivot pin hole
once removed fit the piston to the rod line the pivot pin hole up on the rod and lever and adjust the piston till it's flush with the end of the rod or a mm longer to allow for wear in the linkages
tis will give you a starting point
another tip is to use a 3/16" punch in place of the roll pin
the spring steel in the lever is designed to keep the lever up with no air pressure and was later swapped to a plastic button in the lever that used friction between the two parts of the lever
Sheridan and Benjamin kept using the spring steel in the lever as they stopped using an adjustable piston rod in the early 60's(sheridans not sure on date for when Benjamin did)