They really aren't held in by anything more than the dash panel. They are sandwiched between the panel and the outlet they sit in underneath. There are plastic pins that extend from the panel that serve to line them up properly. Those pins can break when removing the dash panel and reinstalling, but they aren't absolutely necessary.
Removing the dash panel is not hard, IF you know how.
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98 Riviera SC3800 All stock except gutted air box.
1970 Buick GS455 Stage1, TSP built 470BBB, 602HP/589TQ
Best MPH, 116.06 MPH, Best ET, 11.54
https://www.youtube.com/watch?v=UHCda-t_Jls
https://www.youtube.com/watch?v=sfT2tEO4XcU