Anyway, I haven't tried this, but I suspect that you're right: removing the guid should be enough. Note that you probably never want to worry about the rb as those are the replica buckets. Copying those and the original db_ would mean that you'd have three copies of every bucket (the 2 from the clustered set, and the copy itself). That's probably overkill.
I'll note that non-replicated buckets in a clustered environment (where the index's repFactor is 0) do not show the GUID, so I suspect it's mostly a straightforward conversion. Just be careful about the bucket IDs as well, since each indexer's "main" index (for example) will have bucket 0, bucket 1, etc.
I would try this: Sync the db* to your external location, with one per each indexer, per index. That is, if your index is main, and your indexers are idx1 and idx2, create two new indexes on the target: main_idx1 and main_idx2, and sync the respective db's into there. Then, when you need to search those, do index=main*, to retrieve results from each, and not have to seam bucket IDs. Further, the index metadata field in the results will tell you which indexer indexed the data originally, if that matters.