Refurbished head? I'd say get a used head and then have a competent machine shop evaluate and give you a quote for a valve job.

Plug the hole: I love the idea of the lead plug, and I would probably leave the remains of the glow plug exactly where they are.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC