Check the battery cables,6 volts require a thicker cable. If someone has replaced the cables with the gauge for modern 12 volts replace them. I had a starting problems with a 50 chrysler and a 51 ford and after I replace the cables with new ones it started like a 12 volt,make sure where the ground cable attaches to the block is clean. If it still has the braided ground cable,replace it as I have had problems with them,I think they were the major problem with the 50 chyrsler and 51 ford. Jeff