if I had your cars I would put a small block in the dart and the 440 in the polara.
No reason to not have a big block in a C body because there is room for it. So nice to sit on the inner fender and have your tool tray and room to get in there and get hands on everything.
I have had big block A bodies before and they are a pain in the *** even for a smaller person who can really reach in. I am having fun with this duster and a 360. Headers on a small block are still a pain even at that.