Not exactly Grand Opening, but commemorating Ground Breakings for new towers...

Didn't scan well
The one on the left says
"GROUND BREAKING
TOWER ADDITION
LAS VEGAS
HILTON
2-14-73"

The one on the right says
"DUNES HOTEL
LAS VEGAS" {on the face of the shovel)
"GROUND BREAKING
JULY 1, 1976" (on the shovel handle)