Heater core replacement?

Removal & Installation

1. Disconnect negative battery cable. Drain cooling system. Remove splash cover around heater hoses. Disconnect heater hoses from heater core.
2. Remove right side insulator. Remove lower instrument panel trim panels. Remove heater core cover. Remove heater core. To install,  reverse removal procedure. See Fig. 9Â.

This is froma olds 88 dleta there is no regency in 1988

Here are the directions I was able to find for you. Let me know if it helps. Also, you got lucky. The heater core is accessable from under the hood and there is no need to remove the dash.

Disconnect the negative battery cable and drain the cooling system.
Disconnect the heater hoses.
Remove the retaining bracket and the ground strap. Disconnect the module rubber seal and module screen.
Remove the right windshield wiper arm.
Remove the diaphragm connections, the hi/blower relay, the thermal switch mounting screws, and all the electrical connections from the module top.
Remove the module top cover and remove the core.

To install:

Apply a strip of caulk-type sealer when installing the module top.
Install the core and module top cover.
Install the diaphragm connections, the hi/blower relay, the thermal switch mounting screws, and all the electrical connections to the module top.
Install the right windshield wiper arm.
Install the retaining bracket and the ground strap. Connect the module rubber seal and module screen.
Connect the heater hoses.
Connect the negative battery cable and refill the cooling system.
Start the engine and check for coolant and vacuum leaks.