Install the new lug in the hole.
Put the lug down on a brass bench block.
Use a rounded-off center punch to spread the lug tube to lock it in place.
Use a large size center punch and round the tip off so it doesn't bottom out inside the tube.
Stake tightly enough to insure it can't turn and the rivet won't interfere with anything in the action.
As a "belt and suspenders" you can put a drop of Loctite Red in the hole before staking.
You'll probably have to shape and trim the lug slightly so it won't interfere with the cylinder opening and closing, BUT, make sure there's enough lug so the cylinder can't override the lug and fall off the yoke.
Just look at how the original lug is shaped.
Pull outward slightly on the open cylinder and pull slightly to the rear to insure it can't override the lug and slip rearward.