For my 69. I just installed these
Used Crutchfield for the ir exceptional customer service. The original speaker had 2 screws holding it and 2 1/8” clearance.
The JBLs connected fit perfectly and are under 2” thick. I supported them additional with a support tied to the back of the dash.
I am getting the original AM radio converted to a bluetooth product. They recommended protecting the speakers with bass blockers. Crutchfield had these:
Crutchfield Bass Blockers
Pair of inline frequency filters (600 Hz cut-off)
Very happy with fit and stability. Sound awesome.