Sounds to me like lack of lubrication. Normally this is a result of low oil pressure, so as soon as you can get the engine running check the oil pressure.

Also check the lubrication holes for the lobes in the head casting are'nt blocked, as this kind of failure is common in CVH heads that have sludge build up in these holes.

If all this checks out fine then the only other cause of this failure is incorrect tappet clearance on that lobe. If the tappet gap was too tight it would result in constant base circle contact and eventually cause follower damage like you describe. Like wise an excessive clearance would batter the follower face, but this is probably unlikely as you would have heard excessive clearance before the failure occured. Remember too tight a clearance causes as much damage as too large a tappett clearance!

Hope this helps.