Mark the position of the iris plate in relation to the lens casting.
This will allow repositioning of the iris in the exact location.
If you do not do this, the f/stop will be off resulting in poor exposures.

The snap ring is shown partially removed. Note the sealing lacquer,
which was cut with an exacto knife

The iris can be removed without taking the rear cell off. I do not recommend this
because it is difficult to remove and reposition only from the front.