It is always risky to do this, since the bottom of a new lifter is
"Parkerized,"  i.e., hardened, and somewhat rough.  Two Parkerized
surfaces wear into each other during break in, but one (two in the
Vanagon's case) rubbing against a cam lobe whose hardening has worn
through will eat it fast, as you have found out.  The hardened layer is
only a few thou thick.

You might as well go the whole nine yards now and rebuild the bottom
half, or get a complete rebuilt engine and use this for a core.

Stuart