12:1 compression on pump gas ?

In my opinion the reason there are so many conflicting opinion 's on this is if you are reading the number off the piston box, or listening to the guy at the parts counter you have NO idea what the compression ratio is. Things like deck height ,gasket thickness and so on mean more than a generic #.
The only way to tell what you have for a compression ratio is CC the cyls. and chambers. Trust me it very seldom is the same # as on the box. I would worry why a race S-10 with this motor was running 13's.
A one piece seal block probably was set up for reverse cooling ,will that work out with older heads?