Technical Pontiac Edelbrock EP4B intake manifold water passage question

I have an Edelbrock EP4B intake manifold for a 1955 to 1964 Pontiac V-8. There is a hole on the front of the manifold, right below where the thermostat goes. This hole is a connection to the water pump on later engines but there is no connection on my 1957 water pump. Has anyone used this manifold before and ran into this problem? How did you seal the hole? There are no threads for a plug and a Welch plug or freeze plug won't work because the hole is not deep enough. The attached photos show the manifold and also shows a 1961 Pontiac engine that had the water pump connection.

 

I would drill and tap it an NPT tapered thread. Then use a tapered plug screw and teflon tape. The size tap relies on what size hole you have right now. Then I would drill and tap one size larger.

 

here's a plug screw...

 

Gas Tires oil is right. You can pipe plug the hole. Are you going to have a recircuiation hose ? If you are going to street drive this car , this makes the thermostat work properly.

 

I was planning to simply tap the existing hole in my Offy dual quad manifold but after taking a good look, the hole is cast at a severe angle..can't tap or even drill and tap. I'm still trying to come up with a good solution to this problem.

 

for racing its not uncommon for us to drill and tap it for a 3/8 npt plug , use a aluminum one when you do this not steel as it will cause it to corrode( at the threads ) later and fail .do not use tape, use a liquid sealer to keep it from trying to crack the casting and it only has to be flush of the outside edge of the casting not he inset . you can make a by pass by tapping into the top of the manifold ( use one of the already drilled holes ) and plumb that to the heater return line on the water pump or radiator , you do not want to dead head it as it will bend the thermostat causing it to stay closed or cavitate the pump and cause a impeller failure or blow the gaskets out of the manifold head faces . if it takes too long to warm up , make a restrictor in the hose by either soldering a washer with a 1/4" opening into a peice of copper pipe or if your using a radiator with a return nipple solder it there.

 

here is mine 1967 400 engine 1960 frontcover tapped onesize bigger than exsisting hole.
work just fine.

 

Problem solved. I drilled the hole out to 9/16" and used a 3/8 npt tap to thread the hole. Then used an allen pipe plug. Thanks to all of you for the suggestions. HAMB is the greatest!

 

That's the HAMB. An archive of knowledge to help ppl solve problems. Years later.
I just found one of these Edelbrock EP4B intakes to use on my 57 Catalina's 347 and was wondering about that hole!