How can I identify which neighboring houses are fed from the same distribution transformer?
The only way to tell for sure it to shut off the transformer and see who lost power. I obviously can't recommend that "solution".

Another problem is that even if you can tell you're on same transformer, it still won't be a good indication if it will work EOP.

The only reliable way is to plug in the adapter and try. You probably can do it for (almost) free: in most jurisdictions law allows consumers to return undamaged goods purchased remotely (eg online) for no reason. Check out if you're eligible. If it won't work, all you risk is 2-way shipping fee. Just make sure you're making the purchase as a consumer and not as a business entity.