So I recently borrowed my buddy's angle grinder and used it on my Ace classic baseplate kingpins and made the mistake of not setting the nut and ended up grinding them down a little too far. The only backup baseplates I had were from the AF1's that I didn't care for, so I did the same with them and this time I set the nut. It melted the nylock inside the nut and also the top bushings, then I had to let them cool down and take everything apart and scrub the crud off the kingpin with a wire brush. Seems like the slight difference in geometry causes the AF1 kingpins to sit pretty damn high with a classic hanger on em, so in the end it offered some help with clearance but not too much since my hangers are ground down pretty far.
This is my first time trying the angle grinder method and I think you can buy em for pretty cheap. It's still a slight hassle having to mess around with your trucks that much, but I think it may be the better option compared to the inverted kingpin method. No hammering, JB welding, etc. Just grind the kingpin down and then use a shorter top bushing and you're good to go. Oh, and if you keep the grinder level and pay close attention you can make sure the nut catches the threads afterward and you won't need a thread die. Hope this helped any other truck maniacs, shalom.