I'm thinking that may be a Tecumseh HH120. Model number should be stamped in the top of the shroud. If it is, the part number for the cyl. head is 33034. Did a search, and seem to be plentiful, but pricey. Saw a few anywhere from $82+change, to $86+ change. Head gasket was under $5.
Just do look for the number on the shroud to find the correct model, then do a search for that models parts. More than several exploded view diagrams, with part numbers to look it up. Always use the part number when looking.