[ricard]

If the heads are far out of alignment it should be visibly evident when looking at them with tape in the machine. It may help to make a piece of clear tape by removing the oxide using acetone. Normally the tops of the pole pieces for the playback and erase heads should be almost flush with the edge of the tape - the service manual may list exact measurements. I think the playback head should be a fraction of a mm inside the tape, and the record head flush (and the erase head hanging outside a smidgen).