In a careful hurry I checked the 4 m transverter if it is suitable for SSB traffic.
Since it must be driven with 100 mW, a 7 dB attenuator was built so that FT817 500 mW would not fry the mixer stage. A "real-world" 7 dB Pi-attenuator consists of a 2W 120 ohm resistor across, 47 ohm straight, 120 ohm across. I used standard carbon resistors and a quick check with MFJ-259 reported a 1.2:1 SWR max up to 170 MHz.
With full manual switching I listened to my whisper transverted to 70 MHz on a different receiver and it sounded good.
This was the "GO" signal to start planning for a sequencer (probably embedded into one of my I-F-R-K accessories) and a suitable box: this time I will have to do the mechanical work!!