1970 340 has the 1973 low compression pistons

the only way to know what you have is to actually CC your heads.
This is correct mostly because those heads are now pushing 50 years old and who can say how many times they have been thru the machine shop.
As you can see, I did not include any specific numbers for any of the players. My post was just to show what it takes to get to the rated Scr with a 340 and what happens after you install the cam.