Take a close look at the lobe that has ben running against that badly worn lifter- - - -I'd be surprised to find that it doesn't also have some noticeable wear. Some people claim that lifters need to have a slightly convex shape (middle higher than the sides) but a brand new set of "milk can" solid lifters we put into John's 261 were completely flat across the bottom. A concave lifter is definitely too worn to reuse, so it should be reground or replaced. If your old cam isn't showing noticeable wear on any of the lobes, it can probably be reused with new or resurfaced lifters- - - -just do the same kind of break-in run on starting that you would do with a new cam.

Edit: resurfacing lifter bottoms shouldn't be beyond the capability of any machinist who is worthy of the name. It would only take me a couple of hours to fabricate a fixture capable of putting an acceptable, repeatable radius on the bottom of a set of lifters in my little backyard machine shop.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!