jdm p30 piston dome=6.93cc displacement
us pr3 piston dome=6.01cc displacement
They are the second and 3rd HIGHEST domes for b series pistons, only the b16b is higher at 8.63cc unfortunately you cant run the pct pistons with an LS head
p30 is the way to go for cheap pistons, but difference between them and their US cousin is marginal at but can mean alot if you want every bit of compression you can get.