Over on the PY site most people frown on using the 557 block because they are a thin casting in the mains and considered very week.

As stated above the 6X-4 350 (and 77-79 T/A 6.6), 93cc, 2.11/1.66"
6X-8 400, 101cc, 2.11/1.66"

If the 6X-8 heads were milled .050 to get 91cc and 0 deck would be about 8.8 compression with a 041 gasket. With a .027 head gasket you would get 9.02 compression.