Another thing that might be done with a "stock" (9MHZ IF) '301 is to redesign the Filter Unit entirely, adopting a Jones approach such as Ten-Tec and Elecraft have done. 9MHz crystals are common and can be pulled a bit with the right combination of capacitances in series or parallel with them.
You could use varactor/resistor networks which are controlled by mode switching signals or use a panel-mounted control as a VBT of sorts. A TX-signal override would automatically adjust settings for AM or SSB audio bandwidth when the rig goes into transmit.
Perhaps one can refit 9MHz Ten-Tec filters too.
Just thinking aloud here.
73 - Fred, N8YX
