Help me win this argument 400 in a 72.

Did the OP ever state how much money he is/is not working with? Or the given purpose? I can't recall if I actually saw it in here.

I bet if you start off with rear axle as mentioned earlier in the replies, and suspension mods to make it more compliant on the road (e.g., sway bars, new leafs/T-bars, poly bushings, leaf sliders, etc.)-and I'll admit the caveat I don't know your spouse-but she would probably enjoy driving it more-even with the basic 318. Then you could decide from there...

Of course, this is coming from a guy looking to drop a 383 in his '72 Scamp :)

Just my .02...