John,
It's a tough call. There are a multitude of tests to check out starter current draw, and voltage drop across connections etc. I am sure you just want the thing to run. If you bought the 12 volt coil, rebuilt the carburetor and got it running, you could get the cobwebs worked out of it, then figure out which way to go.
Seven 10 second cranks is some pretty hefty cranking. A engine is usually only tight after an initial rebuild. Hard cranking with a KNOW good battery is usually poor connections, undersize cables or a worn out starter.
If you do all your carburetor stuff, put in the 12 volt coil (cheap) and get it running nicely, then you could address the 6 volt hard start situation. If you do it this way, you will be running off the battery so extended road trips will be out!
Maybe someone else has a different take on this deal.
Stuart
