This isn’t that hard for a do it yourselfer but I’ll guess ten times as many people have access to a drill press over a lathe. To square the throttle body to the spindle mount the throttle shaft in the drill chuck, slide the throttle body over it, and mount it to a block of wood. The general rule for reaming is half the speed and twice the feed of what is used for drilling which also applies when enlarging a hole with another drill. Since the throttle body is made of cast iron and the shaft of steel the wear will be biased to the iron allowing re use of the shaft at least some of the time.
