If you are going to pour a footer or pad, I would install the anchors in the new pour and if you ever wanted to remove them, cut them off. A all- thread bent at a 90 degree would be the way to go. Drill holes in the existing concrete and install rebar to hold the new pour in place. Cut a template out of wood to match the base and insert the all thread anchors into the wet concrete. Just make sure the concrete is set before installing the lift, maybe 30 days.