in what order do I put on the firewall insulation pad, heater box, pedal assembly and wire harness . this is for a 66 4 speed non AC

Having done so on my '69, I can't imagine a '66 being a whole lot different. Do the pad first, you need all the elbow room you can get.

The insulation pad is the first thing to install.

Everything else goes on top of it.

ok thanks that is what I thought. my fun is just begging on putting my car back together after having it painted