Since you have a locked distributor and it is running but running horribly, more than likely your dist is off one tooth in either direction. This will cause it not to run at all or run badly. You can try the new sensor but I'm gonna bet that isn't going to help. When putting in those damn locked distributors, most of the time even the dealer mechanics have to drop them in 3 or 4 times to get it right. (Took me 6)