To find it, you'll need to:
* Consult a repair manual: A factory service manual for a 1977 Buick Skylark is your best bet. It will have diagrams and precise location information.
* Look near the fuel tank: This is the most common location for fuel filters. Follow the fuel lines from the tank to see where they connect. The filter will be inline.
* Look along the frame rails: Fuel filters are often secured to the frame. Look carefully along the frame rails near the fuel tank.
* Check under the car: You'll likely need to get under the vehicle to see it clearly.
Keep in mind that because this is an unusual engine/car combination, finding photographic evidence online might be difficult. A repair manual is your best resource.