love the sound of the amp
wonder if anyone has ever come accross a faithful recreation of it in pedal form
i know helix have a model of the Victoria electro king which is in itself a recreation
I haven't seen anything like that, but you might have some luck modifying one of the runoff groove designs to have similar gains and frequency responses in the different stages.
It's not a GA-40 but here's a GA-5 emulator layout.
http://guitar-fx-layouts.42897.x6.nabble.com/Gibson-GA-5-Emulator-td48583.html