Make a drill guide by taking a piece of round stock 1/4" larger than the PTO shaft and bore it out on a lathe until it will just fit over the shaft. Bore it at least one inch deep to give support then cut it off 1/2" longer. Drill a hole in the center of the guide with the size drill bit that is required to drill for the tap. Slide it over the PTO shaft then use it as a guide to drill the hole in the center of the PTO. Use a new cobalt drill (Cheap, from a hardware store) and make sure you are straight. Drill 1/4" deeper than your bolt that is to be threaded into the hole when done.
When you tap it make sure it starts straight. Use lots of oil. Go in a few turns then back out, clean off any chips, repeat until it is deep enough. Don't force it, if it breaks off you are screwed. Only use a new tap. The most expensive tool in any machine shop is a dull tap. I have seen taps break off in a part that has $1000 worth of material and machining time invested in it.
If you want to tap this and cant get a guide PM me and I will make you one, no charge. I need the PTO size and the tap size that you want to use on it.
