71 Dodge Dart 273 swap to 318

if you insist on running the 727 the yes, you will need to have the stock drive shaft shortened and rebalanced
(or have a whole new one build)

now, if you want to keep the 904 you could get a V8 belhousing for it and call it good

A slant six auto trans won't work on a small block. Manual trans will if you swap the bellhousing but autos have a one piece case. Right?