Looking at a very nice 55 'Bird driver. The car is equipped with a porthole top. Guy swears it's original. Did Ford offer those tops in 55? Thought it was a 56 option.

 

I am not so sure. I am positive '56 had them. I also recall most all '55 birds had none. If it did come out in '55 (likely very late in the year) it would be able to be traced simply by the part date code. Also remember the '55 is a smaller car then the '56 so there might even be a size difference there that corresponds to the porthole sizing for each car, thus making each individual in size as per year. Get a good look at a regular '56 porthole and compare for reference or hit the part books for a reference number. I have a Ford parts and accessories catalog (I often forget about) but it only covers 1928 thru 1948. And I can tell you more about '56 birds having worked on them more than '55's.