Prices are coming down on the lithium. I just ordered an Antigravity ATX20 Battery for $369 with free shipping. 780 cca, 25 amp hours, under 5 pounds. It's getting mounted on the inside of the framerail, very close to the starter to save the weight and voltage drop of long cables. They said a standard alternator will charge it fine, as long as it doesen't discharge to under 10.5 volts. If it goes under 10.5V, it shuts off and a special charger is needed to wake it up. So I am putting a sensitive digital voltmeter in the car.
I have a 7 year old dyna-batt that is 14 pounds and will start a car, but I don't trust it 100%. So I will build the battery box to fit the anti gravity and the dynabatt, and bring the dyna for a spare.

I'll let you know how it works out.