The initial camden tablets or sulfite prior to pitching your yeast is typically done to kill off any wild yeast/bacteria that may reside on your fruit. You need to kill these off because they can make the fermentation unpredictable giving off flavors or turning your wine.
This recipe ferments down to SG of .998 My understanding is for port you would stop fermentation around 1.040 - 1.030 SG to retain sweetness. This recipe doesnt call for any sweetening after the initial SG of 1.115 (if I remember correctly) Does the final result have all the characteristics port?
