All 2.6 manual motors are wide blocks all years. The main difference is in the layout of the intake studs on the head - up to 82 is one style, 83 - 89 is the other style. Your 81 will be the early style head. To identify the head style, look to the right of the thermostat on the head - if it has 2 bolts, it is an early style, 1 bolt is later style. All replacement heads I have seen are the later style heads. The later heads run with flat top pistons, early style heads run dished pistons. If you get the 83 up gasket set, just buy the intake gasket separately - they are on ebay. Also replace the head bolts - they are torque to yield and cannot be reused.