No idea about the struct replication side of things, interesting if you can customize replication like that though.
But are you sure your UChunkModel component is itself being replicated? How do you create the model you pass to SetModel? It looks like you’re not creating it as a default subobject in the constructor, in which case I suspect you’d need to override ReplicateSubobjects in order to manually replicate it.
If you can just create it using CreateDefaultSubobject within the actor’s constructor, it would be easier.