If you fail to source an 850 Spider cyl. head, you could widen your search to include the 850 Sport Coupe (same engine) or the Fiat 127 , 903cc ohv version, which afaik is virtually identical. I don't think you guys got the 127 which is a pity because they were produced in their millions which made sourcing a cyl. head easy over here (although maybe not now as people just junked them).
Can your existing cylinder head not be repaired?
Depending on what's wrong, this might be cheaper than the cost of buying a head+carriage+reconditioning.
AL.
