Lifter ID ?

I don't recommend running those lifters with a cam that has a lot of lift. They are basically a stock small block/slant six solid lifter. What happens with a high lift cam the base circle of the cam is smaller that the factory base circle. So when the lifter is on the base circle the lifter can drop far enough to expose the reduced diameter and that allows oil pressure to blead off. . The first 273 engine I ever built (back in the '70's) didn't have oil pressure (cam was .520 lift). I tore my hair out trying to find the problem. Eventually removed the oil pan, and distributer, used a container with oil in it on the pump pickup, and ran the oil pump with a drill. Then we could see all the oil leaking from the lifter bores. As PRH said, use the straight side lifters, unless running a almost stock cam.
PS: The reason for the reduced diameter is to allow less restriction to oil flow through the main oil galleries. I haven't work on a performance small block for years, so I can't say for sure. But I would guess there is a "FIX" for reduced oil flow if using straight side lifters.