What is the difference between the magnum and non magnum exhaust manifolds. I have seen them side by side and they look identical including the port size. Also some of the "C" body right side exhaust manifolds are pretty close looking to the 'B' body with the exception of the heat valve, is there a problem using these on a "B" body car?

I believe the right side C body magnum manifold is the same as the B body manifold.

The non-magnum manifolds are called "logs" because they have a straight run from the front to rear ports unlike the magnums that have an obvious "curve" to them.

The exhaust outlet is smaller than magnums as well at 2" to 2 1/8"

The passenger side HP manifold is the same between B and C bodies. The driver side is different though. C bodies have the outlet between #5 and 7 cylinders while B bodies have the exit at the rear. Outlet size is 2 1/2" for both.

This is a pair of B body HP manifolds.

Here are the C body HP manifolds shown with the late and early driver side manifold below.

Note where the outlet is compared to the B body manifold and the obvious difference to the non-HP logs in the first pic I posted.