Hood clearance

Oh, I just realized that you're going to pull the 273 and put in a 318, correct? There are a few differences between those two engines that you will want to address. Depending on the year of the block, you may have to modify the engine mount brackets. If your car is an automatic, you will need to get a bushing for the crankshaft to reduce the size of the hole the converter rests in. If your car is a manual trans, the 318 may not have a finished crank for the pilot bushing (most automatic cranks didn't get that final bit of machine work). If that's the case, you can either machine out the hole in the crank to the proper size, cut down a bushing (that's what I did), or use the later Magnum pilot BEARING that fits in the converter register. The only other thing I can think of at the moment is that the later smog heads have a clearance problem on the driver's side with the stock exhaust manifolds. You usually have to grind some metal off the head to get enough clearance to allow the manifold to bolt down flat against the flange. If you don't do that metal grinding, you will at best have an exhaust leak, at worst you will crack the manifold. Care must be taken on how much metal you remove and where. Too much in the wrong place and you can break into a water passage. Trial fit the manifold by hand and you will see where it interferes. Take off a little at a time until you just get enough clearance to bolt the manifold down without hitting that protruding section.