Actually just researched a bit more and even though different part numbers the CB250/350K4 will fit your 350F as the part supersedes, which opens up the possibilities for you Eric.
51402-344-670 (51402-333-000)
Earlier USA CB350's and also CB250K3 had almost parallel sided tubes, not the tapered part with three plastic inserts to prevent rubbing. They had a separate collar part . So those parts may fit too (but non-standard)