Hi
If making head for the BB, you can actually use the small box plexi head cab.
Dims are 26 x 8.25 x 10.5"
The only thing different would be the front and back panel cutout, which are longer than the standard 16.5".
I think 18 or 18.5" would suffice. I cant recall right now, but it isnt hard to measure and you dont need to be super accurate. As long as the controls and wordings clear, and you dont exceed the length of plates, itd be fine.
As for tolexing - geez, I wish I know. Thats why I have my cab guy for it! LOL!
But I remember cursing the bejesuz out of him initially. But it wasnt long before he could do it.
Thanks!
Nik