I had the kingpins replaced on my 49 3600 during the ongoing frame up resto. I took the entire axle off and took it to a machine shop. Take the brakes and backing plates off first though. The axle is super easy to take off. You could go ahead and press out the old bushings, and press the new ones in (if you have a press). But to get the proper "slip-fit" you gotta have it honed, don't try to beat the new king pin in, you'll F everything up :p About the oversized bushings... this can all be taken care of by the machinist, he/she will know what you are trying to accomplish.
