Thanks for all the help guys. Being bored out of my tiny today I tried swapping the looms but gave up. Not because its technically difficult but you have to disembowel the cab to do the swap, and on a brand new cab things stick to things, and split when you try and seperate them. Plus when you do get the drivers out the loom lurks behind a stapled pile of nylon floss which I suspect will never be the same again if I tear it from its staples. It was starting to feel and look like a bodge and not a new cab anymore and I stopped before doing too much harm.
So, curiosity assuaged, I shall, as everyone suggests, use it as a 12 ohm cab until we get invited to play Wembley - which can't be long now - or it otherwise runs out of puff.
Cheers, assist-folk.