Before giving up on your 6v system, read Martin's post a few times.

- 00 gauge cable is best, but 2 gauge cable was original equipment (I use 00 gauge)
- every cable/strap should have clean ends
- every place that a cable/strap attaches should be clean metal
- coat all shiny metal contact points with a copper-impregnated anti-oxidant grease

If your cables are old and show corrosion, they could be bad inside the sheathing/covering.

If you want "overkill" do not go to 12v, run the battery positive cable to the hot-lead-connector on the starter, and run the battery negative cable to a clean/shiny/coppered mounting stud/bolt on the starter.

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.