How far can one safely deck a 225 block?

Hey guys. I just got my nice flatties in today. I went with flatties to boost compression, and while in a compression boosting mindset, i was wondering just how much one can take off the deck safely in a 225. I imagine that a 77 motor is gonna have some irregularities in the deck surface that will need to be corrected anyway.

So I have these questions:

1.) How much deck height can be safely removed on a 225?
2.) How much does the compression ratio increase putting flat top pistons in a 1977 225?
3.) How much compression can a slant six actually take?

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