1968 firebird heater core

I have to change out the heater core in my 68 firebird. It looks like a hell of a job. Does anyone out there have any first hand experience with this repair and does anyone know where I can get some detailed instructions? Anything would be greatly apreciated.

Well i am currently doing that in my 80 T/a and it is not a fun job. You just have to start by taking out the dash and go one little peice at a time. It has been a long and slow process for me. But unfortunately i can not help anymore than that sorry.