Lee, just a couple thoughts to add to the good advice above. I see you're in a part of the country where the temp's can get a bit "nippy". Is the truck in a heated shop when you're trying to start it? If not, a 6v system has to be in Good condition to start if temps are in the teens (or colder). Everything has to be pretty much perfect for it to fire off and run. I worked through several winters in North Dakota and when we'd get a warmup from -30 or so it almost felt like summer when the thermometer hit 10 above.
I've never ran a Optima 6 volt battery but I seem to recall they require a special charging technique when really ran down. I'd put a charger on it and make sure it's fully charged. Of course a voltmeter will tell the story too.
Last of all, if the above fails to get it started, I'd give it a whiff of starting fluid. Doesn't take a lot and too much can cause damage. Once running, check timing, and go on a test drive to see if any rough running gremlins pop up and let the tuning proceed.
Good Luck,
RonR
