8 volts is near the danger point when it comes to what the original radio & fuel gauge can take.
The 6 volt system is bullets if everything is in order. Ya gotta have a good battery to start with . I always use a dry cell 6 Volt Optima battery it has twice the CCA of a wet lead acid & about the size of 3 beer cans [ just my own measuring system ] Most slow crank problems in the starter itself [ ru ru ru ru ] in Kook language are caused by bad field coils. Dont forget the 6 volt system is heavily dependent on good grounds. The grounds are as important as the hot connections. I use the braided copper ground cable from the bell housing to the frame & a #1 ground cable from the - battery to the frame along with a smaller braided ground cable from the frame to the firewall. I grind all the frame & firewall ground surfaces to bare metal & slather dielectric grease on them, all grounding terminals are made with stainless steel hardware.
