Is taking it back to whoever did the
distributor an option? Tell them it has been idling rough since they did the work and ask them nicely to have a quick look to make sure they didn't miss something during the job.
HT leads have a resistance of about 15K-ohms per metre. Check this with a multimeter. Bad leads usually go high resistance, so anything more than 20-30K-ohms per metre should be replaced. Bad HT leads give poor fuel economy, rough idle and/or off-idle hesitation and can cause failures in other parts of the ignition system.