"Can you describe what you did Ed?"
These kits come with two sideframes, a sheet metal bolster, and wheels. You've got to drill 5 holes in each sideframe--two for the bolster and three for the axles. I set the sideframe in a vise in a milling machine. Very carefully. I used a center drill to start the holes, and then, very carefully opened the holes up with drill bits.
By using a mill, you can spot the holes very precisely. I think this is why the trucks roll so well. I think if I had done it "by hand", it would have been a disaster. As it was, it wasn't too pleasant getting the sideframes lined up properly in the vise for drilling the axle holes. But once done, I knew all three holes were on a straight line. The bolster holes were pretty straightforward.