I have a 70 chevelle with a 72 motor 396,how can I tell if I have oval or Rectangular heads? When did they change the size of spark plugs from13/16 to the smaller size5/8? :confused:

Sorry,wanted to buy new manifold ,not sure which one to order THANKS

Personally, what manifold is on the motor now? If it is a cast iron manifold, it will be oval port. If still not sure, pull a valve cover and get the head casting numbers to verify what heads are on the motor.

Look at the bolt that attaches the intake to the cyl head. More precisely the four bolts (one on each corner of the intake between the intake ports. IF you have ovals you will see that the flange on the manifold sticks up above the port runners. If you have rectangles the bolt will be more or less imbedded right in the port runners. This is because the rectangle ports are much taller than the ovals. The oval port flange is almost 100 % exposed above the manifold kinda like an exposed inverted "U" shape with a hole right thru it. The rectangle post manifold flange is more or less imbedded in the main body of the manifold runner casting there is only a slight exposed inverted "U".