I have some Aussie magazines from the 80s and 90s that have articles about the Brittens, but there must be some good info on the internet somewhere.
The British MV replicas are/were built by Dave Kay and his son Mark.
George Beale, in England somewhere I think, has built replicas of classic British racing singles, Benelli GP fours and at least one Honda GP multi-cylinder bike; extremely expensive.
Honda RC174 Six Motorcycyle - Motorcyclist Magazine