Although my 'Cuda is a 318, so a little different than yours, I just went through this; maybe this relates to you as well. I had my engine rebuilt and am constantly reworking something on this once-pretty-rusted car. With the new motor in, I was pretty glad to drive it, but noticed in February that I had about a snowball's chance of starting it when it was cold.
After being stranded with a dead battery that got tired of trying to turn it over, I didn't think it was funny anymore, even though the ignition setup was brand new, but '73-style. So I went with an MSD 6AL ignition module, MSD billet distributor, 8.5mm MSD super conductor spark plug wires, and MSD Blaster 2 coil. I bought it all through JEGS for about $500, except the spark plug wires which I bought through Summit for about $80. It starts like a champ, battery stays strong, and I haven't been stranded since.