Two questions:

Why the -+ the scotch tape thickness? Isn't the screen in contact with the film rails?

What do you mean by the mirror drooping? Do you just mean the mirror front is adjusted low, or is it something with the gliding mechanism?

Also, it comes to mind that if there is a small machine shop in one of the cities you drive through, you could talk to the guy there and ask if they could check your caliper for accuracy. They have gage blocks which are highly precise, and they could use them to check at the exact Hasselblad flange distance along with the entire length of the caliper. Offer a little quid pro quo and I expect they'd do it for free.