I cropped the photo of the sign board - maybe this'll be easier to read.
If still too small click of the photo to zoom in on it.

If not -- here is the text from my draft for the sign board
Manufactured during the first week of December 1964
425 Cubic Inch “Nail Head”Engine (360 HP // 465 FT-LB Torque)
2x 600 CFM Carter AFB Carburetors // 2.25 Inch Dual Exhaust
3.42:1 Posi-Traction Differential Ratio (G80)
3-Speed TH400 Automatic Transmission with Switch-Pitch Torque Converter
Of the 34,586 Riviera’s GM built in 1965, only 3,354 were Gran Sports (9.7%).
This particular 1965 Riviera Gran Sport is very highly optioned:
Power Brakes (Standard)..........Cruise Control (K30)
Power Steering (Standard)......Remote Trunk Release (A91)
Power Antenna (U69)...............Radio Reverb (Dealer opt)
Power Driver Seat (A46)..........Air Conditioning (C60)
Power Windows (A31)................Tilt Wheel (Standard)
Power Vent Windows (A32).....Walnut Steering Wheel (N30)
Retractable Seat Belts (A49)...Formula V Chrome Wheel (P05)
Remote Side Mirror (D33)........Automatic Trunk Light (A91)
Rear Arm Rest (D16)................AM/FM Radio (U69)
Custom Trim (A50)....................Rear Speaker (U80)
4-Note Horns (DO5) (see photo below)
1965 Year-Only Options
* Hide-A-Way Clamshell Headlights
* Triple White Wall Tires
* Year-Specific Seat Belt
* Rear Seat Door Handle

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Standard snail horn in lower left corner.
4-Note horns attached to underside of hood.
I recently have been working thru various electrical issues on my Rivi (cabin lights, horn, windows) - decidedly my automotive weak suit.
I made contact with a guy who knows cars and has
8x Buick Riviera Gran Sports. He has a few mountains of spares
