What ever gauge you end up with, try to make it as wide/thick as you can get away with as this will aid in the flow of amperage. As for length of cable, I just happen to have an old cable pulled from a GTV6 which should be the same length for the Alfetta. I measured 188" inches after 3 tries to straighten out the cable and getting slightly different measurements. 188" is the longest measurement. Best bet might be to go 100" + and then cut/clip exess either in the engine bay or back at the trunk/battery.
67 Duetto - Angelina
73 GTV - race car restoration
84 GTV6 - Signore Busso
95 164LS - Black Bomber
"Pay attention son!" - Foghorn Leghorn