First thing is to make sure it will fit the cylinder and the revolver. Each separate from the other before trying them together. Sometimes tolerances stack and they will fit each individual, but not together. Being slightly oversize, as it is, can be a problem but at least you can always turn it down to the factory size and use it if you have to. Also, make sure the basepin latch fully seats as the notch in the Belt Mountain pin is not as wide as a factory unit.
Here it is after checking the cylinder then the frame
And checking that the latch is fully seated.
Then insert the cylinder and cycle the action to check for misalignment between the barrel and cylinder now that you are using a larger diameter pin that has ever so minutely "lifted" the cylinder. Mine checked out perfect weather cocking slow or fast. And it definitely tightened up the "feel" of the revolver.
The next thing is to mark the location of the locking pin, through the hole in the basepin
Then start it with a center drill, and follow up with the proper size bit. Remember the depth stop! zgrin
Then shorten the stub on the pin till it fully tightens without bottoming out in the hole you drilled. This way you have a locking pin that doesn't impart flex on the base pin the way that the standard locking pin does.
From the original photos I took, you can see how long the stub on the screw actually is.
In fact it works exactly the same as the base pin retention system on the newer BFR revolvers.
Then to remove the cylinder, you simply unscrew the base pin lock screw about 3 full rounds and pull the pin forward.