If your lifters are in good servicable condition you should be able to place two of them together, with the flat faces touching & you should be able to see that they have a curved surface as one rocks over the other.
From memory, these things are often ground on something like a 36" radius, so the curvature is very subtle. The cam should also be ground with an ever-so-slight taper across its face when viewed from the side. It's way too small to see with the naked eye.

Refacing them is really just cheap insurance as you will kick yourself if you save a few bucks, only to find later that the cam has an excessively short service life as a result of out of spec lifters.
The basic idea is to have the cam contacting the lifter with a center of pressure off to one side of the dead center of the lifters axis. This allows the lifter to rotate as the cam passes underneath, minimising wear on both the cam & the lifter face.

It will usually rotate the pushrod as well which causes the balls & sockets to wear much more evenly by eventually creating a near perfect spherical contact point at each end of the pushrod, which maximises the life of these components.

As already writen, buying new tappets is also an alternative.


When viewed from the side, a woodruff key looks to be about a 1/3rd segment of a flat disc, cut off in a line parallel with a line across the center.
A shaft is machined with a similar shaped hole parallel with the shaft & the key is inserted. This design allows you to tap the foward edge down a little bit to allow you to install a component, like a cam sprocket, or front pulley, on the shaft easily. Of course the rear sticks up a bit, but as the sprocket slides into position, it pushes the rear part down, which raises the front part up untill the top face is parallel with the shaft.

These keys are used when it is necessary to fit a component that must be in exact register with the shaft, like cam sprockets & front pulleys with timing marks on them. The key not only maintains alignment, but can also provide a mechanical link between the two components,thereby providing a positive drive function