rodent odor problem in my 69 cuda

Febreeze in the cowl area? Spray it in the outside cowl while the heater fan is running to try to get it misted on all surfaces....

If you have a younger kid with a small arm, you may be able to get them to reach farther in the cowl area through the vent to get out more material.

Is the original headliner still in the car? The smell may be saturated into the material.