71 Dart Slant Six w 904 into 64 Valiant

Hey Slant fans. Looking to buy a /6 out of a 71 Dart with or w/o 904 trans and put into my 64 Valiant Wagon. Presently have stock /6 in it with stock 904 trans. Is this potentially major surgery or just an outpatient thing ?

Thanks in advance to all Mopar MD's...…

Will include pics if that helps....