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This had to have been the crappiest job on the assembly line. I had to put my cluster in and out many times and decided to make some mods. Put an extension on the bolts. An allen head bolt with a nut threaded on. That way the nut can never fall off.
Looking from the backside on the workbench, this bolts to a bracket I pop riveted to the console.
Missing from the second picture are two slots I cut into the bracket so the extended bolts will slide into the bracket when you assemble it in the car.
I think there are numerous posts on the subject. This is my solution, its still not easy but feasible.
Addendum: Also missing from that picture are the nuts and washers that actually tighten the two units. That picture was from a trial fit, don't have a final picture. You can spin the nut by hand in the car to get a bit of a grip and then reach in to tighten things with a wrench.