I fitted a Pinlock insert to my visor. I purchased an insert for the XG9 helmet which is the largest Pinlock visor manufactured. It does not have the nasty cut-outs to go around the visor vents and gives a huge vision area.
The trick is to drill the holes smaller than the pins and enlarge them gradually until the pins can be forced into the holes.
Also, drill the holes slightly narrower than the visor insert. Flex the visor flat, fit the Pinlock and when released the curve tightens the insert to make a perfect seal.
If it buckles slightly when curved, cut the groves slightly deeper on the insert until it fits perfectly.
I have a chin guard to cut out wind from the front of the helmet and can sit a traffic lights with the visor closed, in the rain, without it misting.
Finally, don’t be put off by spotty shop assistants who tell you “you cant fit the Pinlocks to the Tour X"