Trent,
These are a reasonably decent flowing exhaust manifolds for a factory set up, but the 283 passenger car is the smaller of the two available. There is also a "Corvette" version that has a 1/2" larger outlet which would give you better flow.

If you have room for these you should also have room for "block hugger" style headers, especially the tight tube from Hedman. They have the four pipes terminating in a semi flat collector that gives about 1 1/2 inches better clearance than the "conventional" block hugger.