Without knowing the internal condition of your Dunlop cylinder, I can't advise you on whether it can be rebuilt.
I have had better luck with the ATE style cylinders - they are simpler in design. Classic Alfa carries them for $170 - their p/n is BR074. Yes, this is more than the cost of a rebuild kit for your Dunlop MC, but it is all-new and again, I feel a better design. Your existing hard lines will fit, though you will need to re-bend them a bit.