So what I learned today is I can probably tap out the oil pan's drain plug to 14 x 1.25 but there are no 14 mm taps in the garage, although I did find a 9/16-18.
I think either is a better route than the oversized drain plugs - and yes I'm still trying to avoid removing the pan - this is just the first time I've got back under the wagon for a few weeks.
After I got home did some web searching and 14 x 1.25 was only used for a few applications but is available.
So looks like I'll have to order taps and the drain plug. In the meantime I'll remove the rocker covers .