Just as you say, when installing my adjustable METCOs (~17 years back) I spied that the threaded shaft spun on the other section which looked all the world like it was only adjustable when disconnected on one side - probably completely removed from the car. The 'jamb nut' served just to retain the pre-adjustment calculated by the manufacturer, so I didn't mess with anything.
IDK much, but the uppers get toyed with ONLY to adjust pinion angle, - sure don't think it's to redesign for dropped driveline interferences. I would cut out the tunnel, install a new snub or even get new coils/shocks before touching the UCAs for that reason.
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear). Finally, wait for it... LT-4 knock module!
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, yes again... LT-4 knock module!