I believe the 70's windows were of different types of glass and thicknesses. My 71 is single pane tempered glass about 1/16" thick. I took a 75 double pane wndow apart and found each pane is 3/16" thick. There is a current thread started by Zepelimum and his glass is a different thickness.
Don't use Plexiglass it doesn't last use Lexan.
As far as the beetles to eat up the crud idea above, an ant farm is more fun to watch.
Sail on silver girl. Sail on by. Your time has come to shine.