The question I’d be asking myself is, how much improvement(ET) would I have to see out of the $1800 head work for me to feel like I got what I paid for?

And then, is that expectation realistic for what they’re proposing?

I’d pay those guys to flow them as-is to see how well the numbers correlated to the numbers you already have before making any decisions about proceeding further.
My preference would be to flow them on as correct a bore size as they have, and with/without a correct sized flow tube.