[R-390] Columbia Electronics SSB mod?

[Tom Norris]

Does anyone on the list have the circuit diagram for the Columbia  
Electronics R-390A modification?  This is the SSB/CW/AM detector mod  
that replaced the BFO control  with a 4 position switch and has a  
small chassis just behind the front panel below the BFO switch.

I'm interested in that or very similar, but should be close as  
possible to that mod.  It's a fairly simple thing, but I'd like to  
see how *they* in particular did it.  Why so picky?  Curiosity.

Yea, I know what curiosity did to that poor little cat...

Thanks

Tom NU4G