Rick,
Owning not a few receivers in my current collection, including all those
spoken of, so far, let me first agree with many of the comments,
including those about the SX-100. Its a beautiful looking receiver but
not without its foibles. A truly nice R-392, SP-600, R-388/51J, et al
currently appear to demand what an HQ-180 would, or more. I'd like to
add to your list the Hammarlund HQ-160. Its not a selectable sideband
receiver, per se, but it is double conversion, general-coverage and,
arguably, a less expensive substitute for the HQ-180. I have a late,
raised-lettering version that works quite well with one of my vintage
operating positions. I have tried several outboard product detectors
with this receiver, to include the Hammarlund HC-10, the CE Sideband
Slicer, and the kit detector from that Canadian fellow. They all work,
although the price of an HC-10 approaches the base price of an
HQ-180A!!! I'd also bet money that you might find yourself liking the
HQ-145A, also a general-coverage, double-conversion receiver with very
respectable performance. Nice thing about later Hammarlund receivers is
that they didn't use many (if at all) paper capacitors. Finally, FYI,
Heath never made an upscale general coverage receiver. Good hunting.