The SL-HF400 and HF600 are
not compatible with your HF860D. The 860D appears to have dedicated motor just for cassette loading, whereas the HF400 and HF600 use the tape threading motor with a belt going from the threading motor to the cassette loading mechanism.
I'm not sure what other models use the HF860D mechanism, though you might want to try
Encompass Parts. That's where I got a replacement gear for the loading mechanism for my HF600.