I bought some replacement lifters from Autozone - Mellings brand and I noticed that there was a diffrence between it and the OEM lifters.

The Melling lifter did not have elliptical shaped cut-outs on the bottom perimeter of the lifter (roller side) like the original. This one was completely circular around the bottom. What do those cut-outs do? Are they some form of camshaft lobe clearancing? I'm getting ready to set the valve lash and fire up the engine, and I want to make sure there aren't any lifter design issues before I do?