If you change out the 273's flywheel then you will also have to swap over to the later bellhousing and you will need a Z bar to fit the bellhousing. 273 exhaust manifold ports surfaces are barely bigger than stock 360 exhaust ports openings, which means you will have to pay close attention to fitment or it will leak. Doug's headers for the early A are recommended. YOU might be able to fit the later truck Magnum manifolds, but not with power steering. I have a set that look like they will fit, but I need to actually put the engine in and see.