Yup to that link. shouldn't need to take the dash off. I've had the occasion to look at the heater core a few times when doing an air mix actuator swap. Looked like ti would come out w/o dash removal.
One thing to note here. I'd automatically have fresh heater hoses and a spring clamp tool on hand. The hoses connect to the core behind teh strut tower in your year. It'* a tight space. I found that the spring clamp tool worked wonders and then the hoses didn't want to cooperate. With such limited accessiblity, I sliced the hose lengthwise and peeled them off the core.
New hoses and spring clamp tool were a key to success.
00 Regal GS: All kinds of cool stuff.