12v Dwell meter and 6v pos ground on Ford?

The answer to your question depends on exactly how your meter is configured. If it is one that requires batteries in order to read dwell, I think there's a better chance it will work. Whether it works or not, you're not going to hurt the meter or the tractor by giving it a try.

Set the points to the specified gap then see what the dwell meter says. It will either say you are at or near the required dwell, in which case it is working, or, the reading will be so far off it is obvious the voltage difference is causing a problem. If the voltage difference is a problem the reading will be off a lot, so don't worry about the meter giving you bogus readings that are just a little off. If the needle bounces against the "0", simply switch the leads to correct for polarity. Good luck...Al English