Looking at both the head gasket and the head pattern, the closest Service Repair manual is the 3T84.
On the Yanmar Tractor Owners Group site are the manuals with the information you need.
YANMAR YM276 SERVICE MANUAL 3T84HA.pdf
And if you want to compare the 3T80 engine Service Repair Manual, then the TM1192 will provide help as well for the head torque.
Link is on my signature below, joining is free, manuals are free. Then WIKI > RESOURCE PAGE > manuals. We keep adding to the collection too from our good community that donates.
Both manuals will tell you the bolt sequence to back off the head and NOT to loose any of those funny caps into the cylinders.
Your engine is a bit rare. Head Gaskets are not impossible to find, but they are far and few. Some people have to order from overseas in the EU from our North American suppliers.
The head gasket you need its very unique too. Don't settle for a generic missing the metal rings for the cylinders. The engine will develop blow-by in a short time.
Our community here on TBN and at the Yanmar Tractors Owners Group will greatly help to keep your machine going for years.
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