I did a complete motor rebuild and plugged that coolant circuit through the intakes with brass plugs 6 months ago. The car runs at normal temperature.

It pulls coolant from the engine before the thermostat ever opens, when the car is first warming up. 

I would carefully grab that hardline between the front and rear intakes when your car is at normal temperatures. If it's hot then you should plug it up. If it's not hot or warm don't worry with it. Replace the metal fuel rail with rubber fuel line like Jeff suggested. We learn from race proven ideas. 8^)

The next time you drive your car hold this tube. If it's hot, plug those lines. It circulates coolant through your carbs through these holes.

I took these pictures of my engine block, manifold and both thermostats. It is my understanding that if i can touch the tube you are showing and its not hot, i should only replace the metal fuel rail with hoses. if its hot, i should plug the exits as shown? what size of brass plugs?

Yes.  I would do both if it were mine and I was having problems with percolation.  Take one of the old fittings to the parts supply and match it up.  I used brass NPT 1/8 I think but don't really remember, take the old ones for comparison.  

EDIT: Looking back I see I used the old threaded plugs off the balance tube but you can get brass plugs at any hardware store.

I started on the passenger's side, that hose pulls from the rear intake.  Plugging it at the water pump eliminates the metal tube running behind the head to the rear intake, threaded plug goes into the intake.  Picture #2

Then plug the front intake,

Then plug the thermostat housing,

 

 

 

Question: Will accomplishing this modification cause any overheating of the engine block? Will the temperature gauge reflect less than 1/2 when the car is at idle on traffic jams? i wouldnt like to be stuck on traffic and then all of the sudden my engine will overheat. In conclusión, is this safe for the engine or not?

Completely safe.  The engine won't know the difference.

On ‎11‎/‎29‎/‎2016 at 10:02 PM, siteunseen said:

The next time you drive your car hold this tube. If it's hot, plug those lines. It circulates coolant through your carbs through these holes.

Yeah!! I tried this on sunday and it does get really hot!!

On ‎12‎/‎01‎/‎2016 at 1:18 PM, siteunseen said:

Yes.  I would do both if it were mine and I was having problems with percolation.  Take one of the old fittings to the parts supply and match it up.  I used brass NPT 1/8 I think but don't really remember, take the old ones for comparison.  

EDIT: Looking back I see I used the old threaded plugs off the balance tube but you can get brass plugs at any hardware store.

I started on the passenger's side, that hose pulls from the rear intake.  Plugging it at the water pump eliminates the metal tube running behind the head to the rear intake, threaded plug goes into the intake.  Picture #2

Then plug the front intake,

Then plug the thermostat housing,

 

 

 

Well i did my last test driving the car last sunday. Cranked the engine pulling the choke lever for one minute. Drove to my dad´s house, open the Hood and touched the tube going accross the manifold and pointed on the previous picture. It was really hot! Let the car rest for 1 hour while i had lunch. Crank the engine and after i got home i let it idle at the parkway for 10 minutes. The temperature gauge increased from 1/3 to 3/4 but no further and the idle started to become sluggish lowering from 900 rpm to 600 rpm randomly with the AC and lights on! Is this normal??? I have no AC compensator. Do you really think that plugging the front intake and thermostat housing solve this problem?? This only happens at idle!!!! I am trying to simulate if i where in a traffic jam and it were raining! My dad thinks it could be the Schneider 274F cam which is not the stock cam and on idle could also cause the rpm to oscillate randomly. He is no mechanic but at least an engineer!!

http://schneidercams.com/274FL6.aspx

I have a pertronix electronic ignition coil also installed!

1 hour ago, jalexquijano said:

Well i did my last test driving the car last sunday. Cranked the engine pulling the choke lever for one minute. Drove to my dad´s house, open the Hood and touched the tube going accross the manifold and pointed on the previous picture. It was really hot!

Do you really think that plugging the front intake and thermostat housing solve this problem?? This only happens at idle!!!!

Yes.  

Ditto

Yes, stop that heat from circulating through your carburetors.  All you need is the 1 minute of choke at start up.   

Mine's been plugged for awhile now and runs great.  Engine coolant temperature at idle is 175F, running in my garage.

On ‎12‎/‎01‎/‎2016 at 1:18 PM, siteunseen said:

Yes.  I would do both if it were mine and I was having problems with percolation.  Take one of the old fittings to the parts supply and match it up.  I used brass NPT 1/8 I think but don't really remember, take the old ones for comparison.  

EDIT: Looking back I see I used the old threaded plugs off the balance tube but you can get brass plugs at any hardware store.

I started on the passenger's side, that hose pulls from the rear intake.  Plugging it at the water pump eliminates the metal tube running behind the head to the rear intake, threaded plug goes into the intake.  Picture #2

Then plug the front intake,

Then plug the thermostat housing,

 

 

 

Okay! Im doing this on Friday! Anyone knows the dimensions of the brass plugs? Any other alternative than cutting the hose and plugging as shown on picture #1???