Just purchased 2.0 Pinto engine
Cylinder head has (1) stamped on
adjacent to No 4 spark plug
Does this mean anything ?

First one they ever made, blimmey have you got an old one.
Havn't got a clue.

Are you sutre its a 1 ?

Unleaded head stamps by No 4 plug for 2 litre heads are L,P,PP,R and RR so it could be an L.