I would do as another suggested and CHECK to make sure you have FULL 12 volt to the dist. not going through a ballast resistor. I just did what you did and changed over a motor from a 305 to a 350 and changed all the parts over and the truck missed and ran badly. I ordered a new dist that is in the garage know. The truck is new to me and I found the alternator was nto wired correctly and not charging and as w worked on the new motor the voltage dropped and the truck was missing and I thought we had a bad spark. ordered the dist. When I fixed the alt problem the voltage went up to near 14 volt and the truck is not missing any longer. Do as the other fellow said run dist to bat 12 volt source with a good wire size 12 or bigger wire. Ed ke6bnl