Ha, crazy thing.
I have it hooked up to i2c-7, but with the Vcc line disconnected from the 3.3V grove and hooked into a 5V. Now its working. Well, at least its detecting consistently, so first step – and that is running at 375 kHz despite the part spec listing max 100 kHz.
Nothing on i2c-0, even though that one should work better (at least it should when I have it clocked at 100 kHz).
Looks like it is probably a bad idea to keep it hooked up that way since there are 10k pullup resistors to 3.3V at the level shifters (BSS138) and 4.7k pullup to 5V at the ds1307 and no diodes in sight. So this actually connects the 3.3 and 5v together. Probably ok to just remove the 4.7’s from the ds1307 since it spec’s logic high as anything over 2.2. Edit: Yep, still works with the 4.7’s removed from the ds1307.
Now I have it working on i2c-0 at 5V. Guess it didn’t have enough drive to pull the data line low with the 4.7k’s in place.