Swapping pre 74 slant six engine to 75 + engine

Yes new engine definitely has emissions gear on it something I'll look into. I'm planning on rebuilding the original and run the car with the newer engine till that gets done I'm in final stages of cancer treatments and jut want to enjoy it for awhile I have most all parts for the rebuilding just not gettyap to tackle it right now. I'll picking your brains from time to time off and on. Thanks Jim