the power valve opens at a given vacum drop/rate and feeds the main system, in your case the pv would open at or below 6.5 manifold vac.
at cruise there is a lot of vacum, too much for the pv to open.
to find the correct rated PV is to know the manifold vac reading at idle in gear, a/t uses the half of of the manifold vac reading with m/t being only 2 rates below manifold vac reading.
so if you have 8in vac at idle in gear [a/t] you would want a 4.5 power valve, which is half [pretty much] of the 8 in reading.
jetting is simply going from ootb, considering elevation, and leaning till a surge at cruise then go richer 2 jet sizes-primary.
If you have a PV in both pri/sec, then you just square up the jetting=same pri/sec. If you only run 1 in the primary, then go 8 jets bigger on the secondary.
