Here are my notes from my heater core install. Allow 2-3 hours.
Heater Core Replacement: Regal part # 52479872
1. Remove bulb from under hood lamp to prevent battery drain.
2. Remove cowl seal.
3. Disconnect electrical connector from A/C accumulator.
4. Remove high fan relay. (2) 7mm screws
5. Disconnect electrical connector from blower resistor.
6. Disconnect electrical connectors from blower fan.
7. Remove blower vent tube.
8. Remove passenger side wiper arm. (use flat bladed screwdriver to open latch on side of arm, then lift arm straight up)
9. Remove (2) wiper rests (7mm screws) and (3) 7mm screws securing lower windshield trim.
10. Remove lower windshield trim.
11. Leaving hose connected, remove windshield washer nozzle and support. Position nozzle aside.
12. Remove cowl vent. (a mix of hardware)
13. Position electrical harness (disconnected in steps 3, 5, and 6) out of the way.
14. Remove blower motor (provides access for splitting case and leverage for removal). (5) ¼” screws, (1) 7mm screw, and ground tab
15. Remove blower resistor. (2) 7mm screws
16. Remove (2) lower trim supports. (4) 12mm nuts
17. Loosen heat shield (if present). Remove clamp securing heat shield to accumulator. Loosen 7mm screw securing bottom of heat shield. (provides clearance for 2 upper case ¼” crews, next step)
18. Remove upper case (use putty knife between case seams to free upper case from lower case). (4) 10mm bolts, (11) ¼” screws**
19. Remove screw securing ground strap, retainer, and heater core. Position ground strap aside.
20. Loosen clamps and disconnect heater hoses from heater core.
21. Lift heater core from retaining clip and remove heater core.
22. Transfer weather barrier to new heater core
23. Fill new heater core with antifreeze (filling prevents aeration and noise from new heater core). Reverse steps to install. Use a strip type sealer on the top of the upper case along the cowl. Extend the sealer one bolt beyond the (4) 10mm screws removed in step 18, to prevent water from entering the passenger compartment.
**Important. You should have removed 11 long ¼” screws before you attempt to split the case. If you didn’t, you have missed one or more screws. The screw furthest back on the right side of the case may be covered in sealer.