Thanks guys. Honest replies IMHO. This was for flat tappet lifters (.842 Chevy size), no info on the engines, but probably stock stuff, with similar spring pressures as in SBM's .
The context was that a new guy to engines was considering putting some the used hydraulic lifters from his old head into a 40 year old head with a solid cam that had been setting for 30 years. I was saying no way you should do that and then foolishly said it would have a '99% chance' of failure.... trying to make sure this new guy got a sense of the risk. Then the person I quoted above claims to have done it successfully ' a dozen times' but with no description of the setups, and seems to equate new lifter failure as somehow as likely too.
I can't in good conscience let a new guys put his engine at risk. And I have asked how one would qualify a used lifter to be adequately good to re-use; not sure what to think of that matter.