I have to say about disc conversion are fine if you know what you're doing. Safety reasons would lead me to believe that if they lock up you could be in trouble as mentioned the cable must be seperate for the handbrake and pedal including the seperate bias valve.
Secondly if you really wanted to increase better perfromance of rear drums just buy groved drums with EBC shoes much better option! You can buy them from Demon tweaks I think? but its been awhile the last time I did this was on a 1989 Kh Clipper boy those brakes were Sh*t before upgrades!