I'll second Randall and Peter, the TR3 components are easy to rebuild (later model LBC brake parts seem to be harder for the home garage to rebuild). The newer replacement master cylinders are different and replacing them will require an adjustment to the outlet piping. It is minor, but the pipes will need to be bent to fit. The rebuild kits are inexpensive and changing out the seals is straight forward. An inexpensive brake hone and an electric drill will clean up minor pitting in the bores of the master or wheel cylinders.
Replacing all of the flexible hydraulic lines should also be a consideration, particularly if you don't know how old they are. They tend to breakdown internally.
If the front disc brake pistons are pitted, replacing them with new one should also be done. IMHO you should consider upgrading to stainless steel pistons.
In the case of sever pitting in cylinder bores, the sleeve insert is an option to maintain original appearance. Apple Hydraulics, White Post Restorations and Karp's Brake Service are companies that provide the service. I would recommend discussing prices and what you want with each of them first before sending your parts out. In some case you get your parts return, in others you get finished piece in inventory and your go on the line for sleeve inserts. Most offer brass sleeves but some also offer stainless steel.