Steve,
Thanks very much, I really appreciate your reply and photos.
Your info matches with some information I received from a Corvette guy, that I should have a 552 emergency (4-way) flasher, and a 224 turn signal flasher. Seems the 224 is load-sensitive, so it will flash at a different rate (and therefore alert the driver) if a bulb fails, whereas the 552 is a constant-rate flasher regardless of the number of lamps (up to a maximum limit).
I've also been told that the Signal-Stat 175 has also been observed in the fuse block as the 4-way flasher, but am still unsure what the Signal-Stat equivalent of the Tung-Sol 224 is.