Decided "go for broke" --- gently lowered the unit onto the table in front of the shelving where it lives (and onto a piece of carpet material), turned it on it's side (3.5mm front panel connector towards bottom - a better choice would have been 3.5mm front panel connector towards top), and continued fastener removal (in many small labeled bags!)
Got to the point where the two halves are split, but not physically separated.
There are numerous wires (towards the front only) connecting the two halves; only two are UT141-type semi-rigid line (RF to and from the lower unit, I believe.) There appears to be enough slack in the wires (except for the two UT141-type semi-rigid lines) to allow about 100mm of separation without unplugging or unsoldering wires (which represents most of the steps involved in separating the two units by service manual.)
Getting to this stage required removing fasteners along the left and right sides that appeared likely to hold the front panel of the upper section in place, as well as fasteners along the sides that join the two halves. The (diagonal, right side) upper fastener at the front was partly obstructed by a U shaped aluminum section (about 5mm radius). I used small diagonal cutters to chew away some of that until I could remove the fastener. The material turns out to be part of the internal cover that isolates the two units, except for an open area near the center/front. I do not think my small cutting will cause problem.
At this point, the front panel of the upper section would still not separate from the body. Along the back of the unit (between the two units) was a span of thin metal (like top and bottom covers, same type of finish, decorative style) with two screws; I removed that piece (exposing the gap between the two units at the rear), and with this, the two units began to move independently, so I focused back to the front panel separation.
On the next step, I removed the decorative trim from the top of the upper front panel (thin screwdriver to pry away the plastic trim piece); under there were three more fasteners that I removed. Once these were removed, the front panel showed some more possibility of independent movement but still was stuck in position.
At this point (with the rear mid-point cover removed and the two units beginning to move independently), I began separating the two units, but discovered that the two semi-rigid (UT141) hardlines connecting the two halves was preventing much movement. I removed the 3.5mm male connectors from the upper unit termination (one of the two switches alongside the output attenuator). This required temporarily removing one end of two of the local (terminating both ends between the two switches) UT141 hardlines so that I could get better access to one of the two top-to-bottom hardline connectors. Once both of those connectors were removed from their switches (on the top side; no attention to the bottom side of the two cables), I was able separate further the two units (requiring careful steps to navigate the two now-free male hardline connectors.) Although I took some pictures, I will consult the service manual during re-assembly because it is possible to reverse the two top-to-bottom UT141 hardlines.
Once the two halves were separated enough to allow access to the bottom front of the upper section, I found no decorative trim, but three more fasteners of the same type, which I removed. I also saw several threaded (like machine screw end) visible along the same bottom front area, but fortunately these do not impede separation.
At this point the front panel assembly can move freely (still constrained by numerous wires) from the upper unit body, maybe 50mm clearance possible for access to the failed connector through what would be the bottom and side of the unit nearest the connector. The attachment of the internal connector is a simple hex nut, like used on old style potentiometers.
I believe (tomorrow, hopefully) I will be able replace the 3.5mm male connector from the front panel (remove both ends of the UT141 hardline connecting to the output attenuator.
Two photos are attached, one of the partially separated units, and other close-up of the 3.5mm-type switch connectors that are temporarily removed.
