The following link shows an interesting design for a 6m transceiver, with a little bit of work it might be adapted for use on one or more of the HF bands:
http://lea.hamradio.si/~s57nan/ham_radio/ssb_6m/ssb6m.htmlThe block diagram shows a unique switching arrangement for the RF and audio signals within the rig. Not only does the IF signal path completely reverse but the same connections carry both RF AND audio. Sure, we've seen bidirectional transceivers as far back as the FT101 but this, this is different.
Tanakasan