distributor question

Awhile ago I got a running 318 out of a 78 Lebaron to put in my dart.Well I'm just about finished and I decided to take apart the distributor for a good cleaning and rebuild.I pulled the pick up coil off and top plate and much to my surprise ther wasn't any counter weights or springs. It doesn't have vac advance and there's even a plate that covers where the vac diaphram would be.Is it possible to have a distributor like this that works?I know the car ran before I pulled the motor hell I even drove it for awhile.Here is the #off the distributor 4091140 Maybe it has something to do with the lean burn set up?Any inf would greatly appreciated.thanks Mark