I recommend you don't rush to a conclusion of the size you want your cylinder throats to be, or what size your lead bullet diameter should be until you slug your bore and find out what the maximum groove diameter is in your barrel.
Reason is, the bullets you shoot should be at least a 1 or 2 thousandths larger in diameter than your largest barrel-groove diameter.
Otherwise, if the bullets are smaller, you would probably get some gas cutting and filling up those grooves.
-So, in short, get the barrel groove diameter by slugging your bore.
-Whatever that is, add a couple thousandths to that for the diameter you need to size your lead bullets.
-Then that-sized bullet needs to friction-fit the cylinder throats, where you can finger push the bullet through the throats. Not being able to finger push through your throat openings with that properly-sized bullet tells you what size to get the cylinder throats opened to. In fact you would send some of those bullets along with whoever does your cylinder work so you have a nice fit, and not so-tight that excess pressure would smack you in the face.
I'll add that a smart test before doing gun work on your cylinder would be to order a sample pack of bullets that do friction-fit your existing cylinder throats, and load and shoot them.... If you get very small or no-leading, then you won't have to slug your bore, because no-leading would mean your bullet size is indeed greater that your barrel groove diameter as evidenced by no lead in the grooves.
Hope this makes sense.
Cheers,
Crab