And it's always good to look outside the box.
I like your ingenuity.

By the way, I often prefer the small hole gage over the plug or pin gage, which by the way come in plus and minus sizes, so there is a greater range of measurements available with them than you might think.
The advantage to using the small hole gage is that it can/will show you if your bore is out of round, and what the numbers are in that situation. Few bores are actually round.