To start off with we need alittle more info to help you out. I am assuming you have the stock 77 231 V-6 in your car.
You are going to have to do alittle research to find out if you have an Odd fire or Even Fire engine. Buick V-6's were
Odd Fire engines in 1975 and 1976
In 1977 they made a mid year change to even Fire Engines, so depending on when your car is made it could have a Even or Odd fire engine (the split as about 66% odd fire 33% even fire)
1978 were the same as the late 77 Even Fire engines
and 79-87 231 engines were all Even Fire with many improvements Including better flowing "High Port" Heads, and exaust manifolds.
So if you have a Even Fire engine you have quite a few options, including a stock used Buick 252 Manifold, New or Used Edledlebrock, New or used Holley, or even a Used Kenne Bell.
But if it is an Odd fire engine you will be limited to a Holley, Offenhouser, or extreamly rare Kenne Bell odd fire intake.
Use the search on this site for some good prior topics on this subject. We have gone over this a couple times in the past on how to ID a odd/even fire engine.
And just so you are aware by simply bolting on a 4bbl intake and carb you will only gain 5-7 HP and only if the carb is tuned correctly. Also a new Intake gasket will be needed, and what gasket you need is also dependent on the even/odd fire issue.
If you want to get the best around town performance upgrade for your car for the $$$ I would start with a rear gear change. Most 231 Powered H-bodies have a 2.56 rear axle gear for gas milage. I would suggest swapping the highway gears out for a set of 3.08 (so they will fit your carrier) or if you can afford a new axle carrier a set of 3.42 gears. But you would have to take your car to a reliable shop to do this.
Sorry About the long post, I can be long winded at times. But you do need to find out the EVEN or ODD fire thing before spending any money on parts.
78 Sunbird Safari Wagon, 3.8 N/A, 1971 Catalina Freeway Enforcer
77 Astre Formula, some day soon powered by a 215 Buick V-8
1973 4-speed Lemans Safari STOCK!!!!! 1978 Catalina Safari
1971 Lemans Safari/GTO Clone, 1969 Firebird Sprint 301 ci OHC6, T-5, 4.10 12 bolt posi