The distributor is a LoadoMatic, uses a modefied vac signal to advance timing, no centrifagul advance and you must have the correct carb with a Spark control valve. engine should have an Autolite 1100 which will have this.

the distributor does rotate with the clamp loose enough. and should be 6* BTDC

You could have a throwout bearing or worn out piliot bushing causing a shudder, or it could be an adjustment