[Commando]

I am looking to swap out the stock 400 engine out of my 1977 Chrysler Cordoba, it is starting to get tired after I put in headers, redid the dual exhaust, and put in a new Edelbrock carb. I have been looking around for some 440 engines and have found a few but what I am concerned about is compatibility issues. I think one of the ones I was looking at was in a motor home, does this make it stronger, or does it show more wear? I know it will fit as there is a lot of room under the hood, but I would like to reuse the headers and starter as it was the only one that would fit with the headers. I might also like to use some other parts, but I want to know if it is missing one part can I just pull it off the 400 engine? What can't I use, I would say if it doesn't fit don't use it but I want to know if anyone has done this before, how difficult is it? And any other advice from someone with experience would be appreciated.