Changing to Doug's D453s

You're gonna have to move the old pipes. How hard that is depends on how your exhaust system is built. Might not be that bad, or it might involve a bunch of cutting and welding. The Doug's will be much closer to the bottom of the car than the old cheapy headers. They give far better ground clearance. But that also means the collectors won't be in the same spot.

As for install, yeah, the engine has to be raised up off the engine mounts. On my car I also slid the torsion bar back, had the starter out, and even loosened up the steering box on the driver's side. But I have a Milodon road race pan with a big kick out and a Flaming river manual steering box that's a different size/shape than the original box. And 4 speed linkage, Z-bar, etc. So mine has a few extra headaches. On my car it would be easier to drop the whole engine and K, install the headers, and then install everything together from the bottom.