I agree that 440 weight is exagerated. If memory serves me correctly your talking about a 100 lb diff. Put the battery in the trunk, add aluminum intake and headers and that would just about offset I think. That's what I am doing with my 69 cuda fb. I voted for the 340, but all "I" have is BB's. My 318 Duster is a different story.
See the difference for me is that I went stock 318.....then hypo roller motor 340 and then drove my buddies 512 stroker 1970 Charger...what a difference....that's why I went 440.....8)