Don't know if anyone has come across this yet, but it seems to be a very descriptive set of instructions on how to replace your dash panel in your Chevelle or El Camino. Sorry if this is a repeat post!

http://www.ss396.com/pdf_catalog/tech/ssdash/1970-1972_chevelle_dash.pdf

I have this guide and used it to swap my dash. It is very useful.