The "easy out" is the same as the "bolt extractor". If the hole is visible that the magnet sets in you should be able to use that to get the bolt extractor to "bite" into. If not you may have to take a small drill bit and drill a starter hole in the center of it as best as you can, then the extractor should be able to "bite" into that.
I checked my Triumph Rocket Service Manual I have on my laptop but unfortunately it lists a lot of specs and sizes of the different bolts and fasteners....but the rear drive drain bolt isn't one of them....at least on the version I have.
As far as the bolt head size...what happened to the one that sheared off? You should be able to get the size off of that.
And if you can't get a dealer to get you a new drain plug, get ahold of Scot in Exile, I hear he has some of "my stuff" for sale on request, I'm sure he'll hook you up, he's hooked up everybody else with "parts" off of my bike.
Good luck,
Dennis
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