The exhaust manifolds are pretty thick. They are expected to rust and pit. The only time I would replace them is if there was a serious crack or hole. And even then I would use the acetylene torch to repair it first. We just spent a LOT of time looking for some later exhaust manifolds for my buddy's 1980 Trans Am. He had headers that rotted out so I convinced him to go back to the stock manifolds. We were super lucky to snag a set of 1977's but the EFE valve was missing. THAT will be an expensive long search. I have been swapping engines since I was old enough to hold the flashlight for my Dad. I learned much as well as many new curse words. I put the engine/transmission in as a single unit if I can. Working in my driveway that is easier than trying to put the trans in later. I leave off the distributor, carb, starter, alternator, all sensors, all brackets, all cables, and wires, anything that can and will get hung up with 800 pounds swinging from a hoist. Usually the exhaust manifolds can be on but sometimes they catch on the engine mounts. Be ready to remove them if they do. Of course the radiator must be out, trans cross-member can be in but I loosen the bolts in case it needs to be moved for clearance or fitment. I also often find that the legs of the hoist hit the lower control arms. So I place the front wheels on two thick planks. That way I get a precious couple of inches clearance and I can still roll the car forward and back while dropping the engine in. I would rather move the car than the hoist with all that weight dangling from it. You are moving right along and I am envious. I am working outside and it has been raining and cold. I have been busying myself trying to rebuild a tilt column down my basement.