Use a Number 52 for your starter hole.
The pin diameters vary a bit even between the same frame styles and seem to depend on what type of front was factory installed.
The drill size can vary between 52 and 43 and of course you can choose to make the pin slightly easier to punch out next time by using the next larger size drill bit.
Don't determine this by eyeball, use a micrometer.
If I was you, I would buy an inexpensive number drill set, that way you are assured of having the drill bit you will need.
I remove the cylinder assembly when doing this work and you will need a vise and some soft lead jaw pads.
If you are planning to use the pin that came on the original sight then you will also need a cup tip punch to remove it.
You can remove the pin with a standard punch but I guarantee it will distort and you will not be able to properly fit it to the new front sight, besides it will look unsightly on the end anyway.
Secure the barrel in jaw pads in a good sturdy vise.
I use a barrel vise and split rings for this but a good vise and good jaw pads will work just as well.
Heating the area surrounding the pin and allowing to cool a bit also makes removal a little easier.
The pin and hole expand a bit with the heat and then contract as they cool which allows the punch to free the pin without a lot of pounding, a couple good whacks will usually unseat the pin and it will drift free with a few moderate follow-up taps.
Secure the old front sight between the lead jaw pads in the vise, I use a brass squib rod inserted in the bore for leverage and as a convenient handle,
Grip the bottom of the cylinder recess in one hand and the squib rod in the other and pull straight up with a fair amount of force, don't jerk, just pull straight up with moderate pressure.
As the sight begins to unseat you can apply a bit of a rocking motion to roll it out of the sight base.
Once the old sight is free, clean the sight base and degrease.
The new sight may need a slight amount of polishing to get it to start set in the base, don't force it, it should seat with a fairly light pressure.
Make sure the sight isn't leaning to one side or the other.
If it is, you may need to polish the front sight inserts base to absolute flat and reinstall until the sight sits dead straight in the base.
Once you get the new sight to fully seat and not lean, you can then coat the sight bottom with some blue LocTite if you choose and final seat it.
Secure the barrel in your drill press and drill your starter hole.
With that accomplished, choose the correct number drill for your final pin and punch the hole.
Coat the new lock pin with blue LocTite and drift it in with your cup tip punch.
Reinstall the cylinder assembly and you are done.
HTH
