manifold was mounted on the 360 that came in the car. I thought something sounded weird about the engine so I had my mechanic take a look and he suspected a light knock on the bottom end. Instead of risking anything I decided to pull a free 360 I had available from a motorhome and just swapped the intake over along with all the accessories. That way I wouldn't risk hurting the previous 360 and I could have a good core to build up in the future. I did inspect the manifold and it hadn't been damaged or repaired in any way but was not new when I got it.
Also, the motorhome was gifted to me by the 2nd owner who bought it in the early 80's with less than 10k miles on it and he regularly drove it from California to Arkansas and back until he parked it in the early 2000's with 77k miles. I have no reason to believe that the engine was opened up before him and he said that he never had to do anything besides basic maintenance and add gas to the tank. The motor never once gave him an issue.