I’ve grinded into both of my kingpins to the point of both the axle nuts getting to that fused point on my 147 hollows. The kingpins are grinding down flush, if anything the kingpin peaks out a few mm past the axle. It’s been catching on some ledge tricks and slappies, throwing me off from time to time lately. What do yo do when your trucks gets to this point?
It depends how far you want to go or what you have available to you, but angle grinding down the kingpin is the main thing I would do on a board with the kingpin sticking up too much.
If that means the kingpin nut can't fit on, I would also trim down the top bushing, or get a low bushing to use on trucks that are that far down, so I could still get the nut on nicely, as well as still having the trucks turn / tightness the same as I had it before too.
So tools you would need include an angle grinder and a sharp knife, often a kitchen knife to cut the bushings, which for both you do need a bit of patience and work out how to do it best, otherwise you could make a mess of it and be left with bushings that are cut too much or kingpin that you can't work with.
I have done this many times over and I got fairly used to it, but I would definitely urge caution and go very easy with both, just cutting a single mm from the lower part of the top bushing, as well as using the grinder gently so as not to cook the bushings, which can happen if you are going too hard on the kingpin.
Anyway, that is the best solution I have used that others have tried and had success with, so I can send you clips / links and more info if you need, or see if anyone else can help too, before going down that road.