Sure you can, you can even do it with factory parts from any Ford or Mercury 302, but they will be used...You can find them on Ebay and craigslist..Look for a stock 4 barrel manifold and carb....plus the aftermarket is full of them...
Yes. However, until you change the camshaft, you will not effect the airflow appetite or demand of the engine. I even make cams which will give you both a power and gas mileage improvement over the factory cam. And they idle perfectly.(If that is what you want.) I'll also guarantee them.
Use a Spread Bore 4 barrel rather than a Square Bore.(Spread bore carburetors have smaller front barrels than the back barrels.) But some 4 bbl intake manifolds will not accommodate the pattern of a spread bore. The right spread bore 4 barrel will get better gas mileage than your 2 barrel. A spread bore will also have better manners and better light throttle power than a square bore 4 barrel will. One inch thick '4 hole' carburetor spacers are your friend at low-mid rpm's on the street, too. Just make sure it's a spread or square bore spacer like your new carburetor is.
Go to a place like Summit Racing or Jegs and get something like a Edelbrock intake that will accept a 4 bbl carb and the carb. Just changing the intake and carb is not likely to be a night and day difference. To really feel a difference you are going to have to make other changes like timing, exhaust, cam, ect... but its a start. Dont get too big a carb, more CFM does not mean more power, it has to be sized for the rest of the engine / system.