Never, ever replace a camshaft without installing new lifters. Even though you might not see any wear, the lifter face is very complex. The surface is not flat, it is actually convex, which promotes a spinning action as the follower rolls around the camshaft. The result is that the followers actually wear into and is profiled by the specific camshaft. New lifters on an old camshaft can also prolong the life of the shaft!
The dome shape of the bottom of the lifter is intended to keep the lifter rotating as it goes up and down. New lifters should be used any time a cam is replaced or reground. New lifters can even prolong the life of your favorite old cam. This is the stock follower and weighs 46.1 grams.