t-cycle

I would like to replace my front derailleur. The rear derailleur is a Shimano 105 nine speed. The current front derailleur is a triple chain Shimano without a model stamped on it. (I was told it also was a 105, but I have my doubts.) Could I replace the front derailleur with any Ultegra triple, (I’m looking at the 6503,) or are they other considerations I have to take into account in order to insure compatibility?

Thanks!