I got a edelbrock 2104 intake manifold. There are 2 big holes on each side of the thermostat for water outlets, and 1 big hole just behind the carburetor, i am wondering what sizes they are ? so i can buy pipe plugs for them. Is there any other hole i need to plug that i missed to mention ?

 

I thought they are 3/8 pipe = about 1/2 hole

 

Water holes are 1/2" pipe (about 7/8" dia. Hole behind the carb is 1/4" pipe (about 1/2" dia) and will be covered up and rendered useless by a Holley carb, if that's what you're going to put on it.

You'll need one of the holes by the thermostat for your heater. The pass side one is better obviously. Put a brass (NOT galvanized steel or black iron) 1/2" pipe to 5/8" hose nipple in that one and plug the driver's side one. Put your other heater hose to either the top of the water pump, or to the radiator; it'll be a 3/4" hose.

There are no 3/8" pipe holes on the intake.

 

Thank you so much for the information, just what i needed to move forward with my project.
// casey