Something has to be slipping for this to happen, or one of the pulleys is not the correct one(teeth).
It is fixed mechanically so unless belt slipping pulley has to be wrong on auxillary shaft.
Easy way to tell is to count the teeth.
Crank pulley will have EXACTLY HALF the number of TEETH that the CAM PULLEYS and AUXILARY do, as the cams and aux turn at half speed due to the engine being FOUR STROKE.
As to wether the pulley is the same on PINTO and COSSIE I could not say but would have thought so.
The pulleys for the cams + aux shaft will consequently be the same size as PITCH is fixed, has to be for the belt.
How far out is rotor arm ?, thye do suffer from ford itis, that is sloppy fits, but only wiggle a few degrees due to movement in SLOT of dizzy where arm sits, if so just pack out with paper or thin card, yet to meet a ford where I did not have to do this, and cured so many "sensor" running problems due to timing scatter.
tabetha