I had a bit of free time today so I knocked up one of these, the outer thread is M20 x 2.5 with a m14 sump plug, you will need a 17.5mm drill bit and a M20 x 2.5 1st/taper tap. I would highly recommend that you drill and tap in a drill press to get everything straight. As you can see I back bored the inner M14 thread section as I was just buggering around really. It comes with said sump plug and the sealing washers, you will need to lock it in place with a sealing compound.
Now to the price, its free as in bugger all but with a few provisions, you must be a TMF member as in paid your £5.00 and have a post count of over 200 and live in the UK.
Shooter