Also some used Dasan V5824G or V5812G (used) can be used for that.
But you have to be aware of that provisioning between different OLT vendors is different.
There is much more differences also, like firmware upgrade over OMCI - Dasan in example violates G.984 specification...
Huawei 5600 can be unlocked (if locked) - I know method if you need.
In general OLT/ONT interoperability is closer to making phd on university, because there are no enforced standards for OLT tests (ONTs have BBF.247 at least, but it does not guarantee interoperability with all OLTs...)
In general - TR-069 is the best way to keep interoperability, but again - no guarantee without proper ONT vendor support.