Early type series two marster cylinder Change

Another post by me about series brakes

still got a problem bleeding up and my local land rover dealer said about putting a later type master cylinder on at the moment i have a early type with a big nut on the rear ( i have a lwb series II 1958)
the later type have a higher out put and more efficient.
is this true or are they wanting me to spend more and more money?

is it a straight swap to a later master cylinder and will it be later and push more fuild though the system

pretty sure the fitting is the same....its the cylinder dia thats different....at least it was on the 2 cylinders on my 2a