Take it that this is a Original 96er. If so, you should have and EBB as well as two drive-side dropouts (one with a derailleur hanger and one without).

You should be able to go to you local Carver dealer and order the correct drive side dropout if you don't have the deraileur hanger one http://www.carverbikes.com/Dealers/#Auth

Forget the Brompton hub or Sturmy Archer, these are not appliciable for what is a pretty custom MTB, although Alfine 11 may work; but if you have the correct parts, a normal deraileur gear system should be easy to install.

If not, photos please to see what you have