I put a small tab of smooth black electrical tape on the RH end of the snap ring.
Wrap it around the end so it will stick up/out when installed.
About 3/4" long.
Then lay the body down on a folded towel.
Set your lens in the opening and align as necessary.
Start by inserting the LH end in the body just past the 6:00 position.
Holding the tab, 'walk' the snap ring into the groove using your right hand to install the ring while your left thumb holds the
LH end in place.
After the ring is in place wiggle the lens to center it and make sure the ring is fully in its groove.
Repeat on the other side.
The tab will allow you to easily remove the snap ring by grasping the tab and reversing the installation procedure.
Later . . .