That maxim chip would very likely resolve the rx/tx side of the equation ( my only stated need in this thread ;) ) but since this is for a gps unit I plan to also use pps as a part of the time sync for additional accuracy.
Oddly, with pps connected to the cts pin on the ftdi board I don't actually get the pulse registered in the kernel pps driver. I'm going to try out the gpio approach on my pi but my C foo is ... well, very very limited so far. i had posted on this previously and no one responded :-< ( viewtopic.php?f=19&t=36030&start=0&hilit=pi+gpio+pps
Thanks for the hint about the maxim chip!