You will have better success with solid wire and gas for thin metal. Flux core welds a bit hotter. If a $1000 mig is out of your range, consider one of those small 110v units like they have at home depot. One with gas a gas hook up of course. I have welded with them before and they actually work pretty well.
'66 Coupe - 289, T-5, Tri Y's, Dual exhaust, Electronic ignition