Re: Amp back
Just like Mr. B says...
Cabs are constructed to be what they are. Size, speaker, material, joins, design and baffle all contribute to what the cab does. It's not as simple as a box with a couple of holes in it. Taking off the back is the easiest way to check that out.
I would strongly recommend against cutting the back- if you're really into the idea of making a semi-open cab, get another chunk of wood.