the heads on my 396 are oval ports closed chamber #3931063 and the intake is a oval port gm holly he said came off a 427 # 3866948 my question is which heads are better opened/closed/oval/sq /rectangular, and i"am going to take the intake off for a aluminum one

 

the rectangular ports are the hi pro factory heads that came on the hotter 396 and 427's

 

Depending on the displacement of the engine, and whether it is going to be mainly used on the street, or for racing purposes. The square ports flow more air which may be too much for a mild street engine and cause driveability problems, however an all out high revving or big displacement engine over 500 inches can use the extra air from the square ports and make more power than it could by using the oval port ones.