Engine swap?

Considering replacing the tired 225 in my wife's 63 valiant. It has a 904 push button trannny that was rebuilt by a previous owner. The current engine has a 2806830 casting # which tells me it's a 67-74. I would like to find someone's "take out" that is in good running condition. Are all 225's a direct fit? I need to keep this on the CHEEP because my wife says """Why would you replace the engine? It starts and runs fine!!!!"""". I do have to add oil constantly and it does run great. Yeah I've done all the tests, the engine needs rebuilt or replaced,,,,THNX!!! RH
Then share those findings with your wife. Women are different, not stupid.