302 Swirl Port Heads ?

Looking in a 1988 MP catalog I found:

P4452748 318 C.I.D PORTED HEAD
Cylinder Head is fully ported and fully assembled. Features 1.88" intake and 1.60" exhaust valves, and oversize pushrod holes. Offers 55 horsepower gain on H.P. 318 engine. Based on '87 production swirl port design.