Hi Aquila,
My thoughts are as follows: DOT 3 and 4 brake fluid is hygroscopic, which means it attracts moisture. The DOT 5 is silicon based, so it does not. Hence, the popularity of the DOT 5 fluid for our rarely driven collector cars. The two fluids are utterly incompatible, and if you want to change fluid types you must either replace ALL seals or flush the system with alcohol.
I expect that the failed wheel cylinder will have rust pitting internally due to the above mentioned moisture attraction. Usually the rears are the first to blow due to the fact they are lowest point in the system and the water collects there. I would replace or sleeve the two rear wheel cylinders, and possibly the master. Then bleed the entire system until you get good fresh fluid at all bleeders. Then, just drive the car! I don't think that I would go to the trouble of changing to DOT 5. To tell if you have DOT 5 already in the system, look at the fluid colour, the DOT 3 & 4 is brownish, the DOT 5 is purplish. Also, make sure your parking brake is functional and in adjustment, just in case you have a failure again.
Safe travels, and what a lovely car!