The blocks are not the same for p7 heads. Im not sure if any of the xrII blocks are working in builds. You can buy an Ernie Elliot aluminum block for p7 heads that can go to 440 inches.
These block can be made to except P5 heads
Now that might be well worth the extra effort.
P7 Head I don't believe would be any better than a W8 or W9
