[ALERT1]

First Time User Here But plenty of experience with Chevy, GMC...
found a inexpensive Holley 650 Duel line, part number on carb[List 4777 0805]...What does this fit? I have a 1986 GMC 3500 (1 Ton) with a 350 (small block) needs a carb. Can I use an adapter to fit a 4777 to the manifold?

[DoubleVision]

What intake is currently on the truck? A stock Quadrajet intake or other?
What distributor?
If it's a Quadrajet intake yes you can get a adapter and bolt on the Holley. However with open adapters they do more harm than good. The open adapter makes each cylinder draw off the entire mass of the carb which greatly reduces low end torque. These adapters are also known to disrupt the vacuum signal. Edelbrock makes a 4 hole adapter, but it's rather restrictive due to the design. If your intake is a Quadrajet intake, that's what I would use as Q-jets is one of the best street car daily driver carbs ever made. The small primaries give it great throttle response, good low end torque and conserve fuel nicely. The carb number you posted comes up as a 650 Holley Double pumper, which really isn't the ideal carb for a stock daily driver vehicle.

[ALERT1]

Thanks for the info. I do have a Q-Jet, the 1986 truck has a plow and does approximately 30 miles an hour (carb trouble), need to rebuild the Q-Jet, just thought I could improve power by changing. At any rate, thank you for your answer.