440 BUILD TO 500 PLUS HP

[PlumCraZRT]

Just found out my block is not a 70-71 but rather a 73-74 
And read those blocks have a much lower compression ratio. So I guess my hp is way lower then expected.
Was it the pistons or the deck height that changed to reduce compression in those days?
If I want to increase compression, besides shaving the heads, can I shave the deck?
This engine was rebuilt totally 5 years ago and I don'T know what went in it. So compression is unknown right now...
I just have an invoice from previous owner that says 270h comp cam and 6 pack pistons.

The pistons would have determined the compression ratio from the factory.  The blocks' deck height never changed.

[Chryco Psycho]

the 6 pack piston is 10:1 if it is flush with the deck , the deck are always high tough so figure on mid 9 :1
 yes you can shave the deck to get the piston flush but make sure you know what heads you are using before doing that or you coul dend up too high , especially with a close chamber head & stroker kit