I have a 10" and a 6" spotted gar and I feed them frozen krill and earthworms mainly. They seem to really love the worms. I have also heard of people feeding them freeze dried krill. Mine like their food below the surface. As far as bloodworms, I think they might be to small for them.
once a gar is trained they will literally eat almost anything. if they dont eat it, they will take a damn good shot at it. ive had mine steal chunks of sweet potato from my pleco and swim around trying to eat that for several minutes before he realized he didnt want it. ive also had them eat algae wafers. honestly if you put any decent effort into training it, you can have him eating a very large variety of foods in no time.