Hi Andrew,
I don't have a buyer for just the head at the moment but a previous commenter named fuzzonaut did express a minor interest. (not sure how to tag them in this post.)
Umm about the price I don't know what it would be, obviously looking for £700 for the lot so if it all adds up I don't mind how you and a potential other buyer divvy it up. (I'm guessing the head would be worth a bit more than the cab so I guess maybe a £450/£250 or £400/£300 split? Opinions welcome!)
The main concern I have about splitting it is if one buyer pulls out and I get left with half a peice of kit that i'm unable to demonstrate working to a future buyer, which could cause complications in selling it. Would you consider buying the whole lot and then selling the head on again? (just looked on e-bay and there is a bassman 135 head for sale ending in 3 days, if you follow that maybe the final bid will give you an idea of what the head alone would fetch/how much my cab would cost you, should you choose to do it this way.)
Karim