I dunno Pat, how will you keep the drill bit and tap straight and true? I kinda like the oversized plug better. At least if it fails you can always turn to the drill/tap...
It's a non-stressed (well, other than the torque on the plug) fastener; not super critical to be precise. As long as the hole isn't "wallered" out, it should be OK. I have access to the same tooling that is used for Honda auto parts mfg (I work at a tier 1 supplier) so a good, sharp bit and tap won't be a problem! Just have to make sure that I don't drink too much caffeine before "surgery"!