340 pistons

I don't know those pistons exactly but looking at the design and size of the dome, a no go for a street motor, I find the minute any piston starts having a dome you start being in 12+ on compression (yes exceptions when piston is left in the hole or big chamber heads) if I had to make an assumption those are 13 or more just based on design. There is no hard fast rule for street compression limits but for all street most will stick with 9.5 as a safe number, can go higher (or Less) based a any number of factors (heads, quench, tune, fuel, etc.). These are likely high compression pistons with fairly large chamber heads. I am sure others may have more knowledge about that exact piston.