I'm not a welder nor a machinist but good Lord, how much have you decked those heads?
not sure, had a gasket failure at 15/1 compression.
Not trying to be a WA here but if you had a gasket failure, why do you think it is due to excessive milling? Especially when you are unsure of the amount of milling? What I'm getting at is that if there is some other reason for the gasket failure, drastically reworking the heads may not solve the problem.
Could you get a reasonable guess by doing the old trick of measuring the thickness of a lower head bolt boss and comparing it to a virgin head?
