Thanks to all who posted advice on the blade type switch for my 51. Based on the advise concerning the size of the blade and its ability to carry the current needed at startup, I fabricated a piece out of copper and screwed it to the blade effectively doubling the thickness and area of the blade. I installed the switch and used the car all weekend at the Greenfield Village Motor Muster. The car was started many times during the event and driven to and from. The blade never got hot to the touch and operated perfectly.
Thanks again for your help.