What size are the exhaust studs? 6 mm. or 8 mm.? Is the exhaust port D-shaped or fully round?
RC04 says it is an F motor. If the black paint is original and the side of head wiped to make the silver accents then '81-'82 likely. Pic up a bit further forward to around the oil pressure sensor location, if it has the little raised donut casted next to it then likely an '82.