1992 Oldsmobile 88 heater core

REMOVAL:

Properly disable the SIR system.
Drain the cooling system into a suitable container.
Using a suitable pair of hose clamp pliers, unfasten the clamps, then disconnect the heater hoses from the heater core.
If equipped with manual climate control, remove the A/C temperature valve actuator as follows:

A. Remove the instrument panel assembly.

B. Remove the temperature valve link rod from the temperature valve by snapping it out.

C. Detach the electrical connector from the A/C temperature valve actuator.

D. Unfasten the retaining screws, then remove the A/C temperature valve actuator.

If equipped with electronic climate control, remove the programmer as outlined in the following steps.

A. Open the glove compartment, disengage the stops and swing the door down.

B. Detach the electrical and vacuum connectors.

C. Remove the driver temperature valve link rod.

D. Unfasten the screws and remove the programmer from the vehicle.

Remove the heater core cover screws, then remove the cover.
Unfasten the heater core retainers, then remove the heater core assembly.

No, the dash does not have to be removed. Only what was stated above.