I had the same problem with my 39 Deluxe Coupe, the best advise I received was from GM....quote "Save your money, get some 1/0 cables and it will spin like 12 volts" I did just that and my starting problems were a thing of the past.
Thanks G.M. changed the cables as you suggested on my 1939 Ford 5 Window Deluxe Coupe yesterday to 1/0 from batterycablesusa.com and it started up like a young Thoughbred wanting to leave the starting gate. Great addition for the old flathead.
David
The Villages Fl.