Yes the Celestion V30 are used the most it seems: Marshall, Mesa, Randall, Diezel, ... all have models with these speakers.
Most companies don't tell which kind of wood is used, except Randall, they use three-fourth of an inch thick, 7 or 11-ply, void free birch plywood (multiplex).
I'm pretty sure some other companies use MDF (Medium Density Fibreboard) for some sides, but these aren't water resistant and should be covered with those black sheets they usually paste onto the wood.
First I'm gonna try to find out what kind of wood and speakers would suit and hopefully it will be affordable.
I'll be glad to let you know how it turns out!