In all honesty, you don't need adapter plates, just some RTV where the gaskets from the PI patter differs from the NPI heads our cars have. If you really want adapters, Livernois performance can sell them to you for $300.
-5.0 Big Bore
Ran @ Normal Operating Temps, No Race Tune, No Setup Changes from Daily Driven Configurations
9.0 @ 78 (1/8 Mile only in Abilene
2.06 60' on Street Tires (BFG G-Force Super Sport 245/50/16)
3805 Lbs, Stock Exhaust Manifolds
Density Altitude = 4132'
That Run, Corrected for Standard Day
1/8 mile: 8.75 @ 82