Glove Box Install

[ajsfirehawk]

I'm new to the site back 5 weeks ago when I bought my 72 C/20 Longbed. I was under the dash this weekend fixing and hooking up the heater boxes and a/c duct work. I pulled off the glovebox door, crumbled and removed the remnants of my old glove box. As I began to look at fitting the new one it, it rapidly become quite obvious this was designed to be installed before the heater duct work goes in. It appears I'll have to strip in down to the firewall and expose the bare heater core to get access. Please confirm, and if there is a handy dandy trick, I'd love to hear it.