Pull the valve cover. If the rocker arms are stamped steel and almost as wide as they are long with no adjusting screws on the pushrod end, you have a hydraulic cam and lifters. If the rockers are cast and are sorta skinny with adjusting screws on the pushrod end, you have a solid cam and lifters. Also the end of the pushrod will be a ball on hydraulic and a cup on solids. Having said that, it's not a good idea to put new lifters on a used cam. It greatly shortens the life of the cam lobe...