what size megafuse?

63 dart stock car. blue high performance MP voltage reg. race hei module. pertronix flame thrower race coil. std 70's square back alt. 12V battery behind dr seat. I was thinking of useing a megafuse right at the battery (on pos or neg cable?). I had seen alot of posts regarding megafuses but the amperages are all over the chart. what do you guys suggest? or another route if that would be a better way to go. Thank you for your time. RR