There seem to be 3 options for cab lights on Ford. the tear drop, the chrome tear drop, and the more squared flat base style.

I have an original 1979 and it has the flat base style from the factory.

Is 1976 the same ?

 

EOTZ-15442-D (replaced D6TZ-15442-A) .. Amber Roof Marker Lamp-Rectangular Design with one piece body & lens / Obsolete

1976 F100/880 from serial number A25,001; 1977/96 F100/880; ditto 1997 F250 H/D & F350/880.

Only pic there is...

 

Take a look at the Truck Lite 25760Y. Looks exactly like the roof lights I've taken off of a couple of 78-79 trucks.
25 Series, Incandescent, Yellow Triangular, 1 Bulb, Marker Clearance Light, P2, Gray Polycarbonate 2 Screw Mount, Socket Assembly, Ring Terminal/Stripped End, 12V | Truck-Lite

 

Those are what I bought. thanks guys.