318 Port match heads to Performer RPM Intake

Just dont create a pond in the middle of the stream 'so to speak' and you should be fine.

You obviously see the smaller 318 gasket is a hair smaller than the existing intake port windows...so that idea is out, if that's right.

Open it to the intake, make the heads port windows look like the intake 'manifold' port windows with the gasket in place. Theres the middle.lol
If you use the stock composite that comes in a stock kit... the intake port window on those gaskets are smaller than the HP felpro you have in the pic...

Imo... you are approaching this with the WRONG 360 intake gasket. You want the #MS9..something. cant remember. Hold on..
Fel-Pro Intake Manifold Gaskets MS90109

2.188x1.00 vs 2.27x 1.160
You can 'in the end' use the larger window gasket after port matching with the slightly smaller one.