Some folks like to remove the speaker grille to provide more access to behind the dash and the speedo. Otherwise I've found that using a 1/4" drive ratchet with a bendable/flexible extension and deepwell 1/4" socket will aid in getting that last stubborn nut off.

Here's an example of the Flex Extensions I'm referring to.
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~ Dan
1951 Chevy 3 window 3100
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"My Grandpa Carl's Truck and How it Became Mine"
1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver)
US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)