Large allen head polepieces fitted to L-1000 pickups in 1980.  Note the plain (no Pat. #) cover that was used from 1980-81.

Slot head polepieces fitted to L-1000/L-2000 pickups from 1981-82.

Small allen head polepieces fitted to L-1000/L-2000 pickups from 1982 to present.  Note the Pat. # pickup cover that was introduced in 1981.