What engine for my Wife's 70 dart

Luke, looks like you're on the right path. Btw: Good for you building this for the wife. Very nice of you and very smart. It's always easier on us if the significant other is into the hobby too. There are still lots of 318/904 combos out there. Just be patient and find the right one. It would be nice to find one in a running car (that maybe someone is switching to a big block) so you can hear it run and possibly drive it. GL.