As any other used part it's going to be worth what someone is willing to pay for it.
I don't know how rare that casting is or how important it is to have that exact casting.
I am putting L35 heads on my wife's truck and leaving the stock heads sit.
My ball park guess would be 50-100.00 a head? Once again.. just depends on how rare that casting is.. might want to do some research on syty.org.
Hope that helps,
Scott~