OK, so I guess there was an 075, 175, 275, and 375. I know about the 075 of course, and I've read a little here and there on the 175 and 375... but there just doesn't seem to be much chatter on the 275.
This is basically what I've got (which, no surprise, comes from this site!)
As I mentioned here a while back, I found a pair of 275 drivers with H5040 horns at the "Yankee Swap" pile at our town dump (on the 4th of July). I am still really curious to hear any modern opinion of these, e.g., as they relate to their cousins (or brothers).