Temp sender in the manifold gives a better indicator of overall engine water temp, the one in the head will read higher as the head is right over the combustion chamber.

The looped hose, from water pump to intake, can be removed and plugged at the pump, all it did is send water out from the manifold to the heater originally, and back from the heater to the pump inlet.

You can just plug the under carb water passage if you want, it is there for cold climate carb warming.

 

Ok,Thanks for clearing that up for me.
So just get some high temp sealant and a Bunch of plugs and I should be set!

 

Thread sealant works perfect, get it at your local parts store, along with the pipe plugs too.

 

The looped hose is the thermostat bypass that provides circulation through the pump and cooling jackets when the thermostat is closed. A lot of guys plug these and depend on the 1/4 inch hole from the passenger side head into the block and back to the pump to provide that function. I'm not a fan and do not do it on my builds. Leaving this routing out increases pressure inside the cooling jackets as the pump holds a head against the lack of retuning coolant this risks local overheating with little circulation and risks cavitating the pump as it is attempting to deliver more coolant than it is receiving, so this lower the pressure around the impeller which gasifies the coolant especially if any water is present in the coolant, this puts bubbles into the circulation; 100 percent glycol is much more resistant to this event but unless you really understand thermodynamics it's something I can't recommend unless you belly up to the cost of Evans' coolant system.

If you drive the engine hard as in plowing snow or in competition greater than quarter mile events the coolant tends to boil over the rear combustion chambers trapping steam there. 4 corner return running hoses from the rear of the manifold where it blocks the rear return passages and connecting to the front return manifold insures that doesn't happen. It took the factory a long time to respond to that but many of the intakes since the mid 1980s connect the rear sides and the front to the heater/bypass circuit to eliminate this problem which in turn stabilizes the need for different ignition timing on the rear cylinders which then improves power, mileage, and reduces emissions.

The mid head mount for the temp gauge sender is just ahead of the hottest place on this engine the paired exhaust valves on the driver’s side head. Both heads have paired exhaust valves but the driver’s side is hotter with a standard (clockwise) rotation pump as the rotation favors more coolant to the passenger side outlet. With a factory style serpentine belt rotating the pump counter-clockwise the problem reverses to the passenger side head running hotter at the paired valves so you want to monitor coolant temp there if that's the belt setup. If you're going to blow a head gasket or crack the head it's most likely to happen in or around the paired exhaust valves.

Using the bypass as a source of hot coolant for the heater is simply a convenience for the cabin designers. You will find on air conditioned models that the heater core is not active all the time as it is on non-AC models. But the AC models have a combination valve that while shutting off coolant from the heater core also provides a passage back to the pump that in turn is closed when heat is called for and the valve reroutes the bypass coolant back to the heater core.

Another very good use for the bypass coolant is to use an engine oil to coolant heat exchanger these are pretty standard since the mid 1980's on everybody's cars in one design or another. This greatly speeds engine warm up by heating the oil to the coolant temp. This reduces fuel contamination of the oil, and wear between the rings and cylinder wall by getting the choke mixture enrichment shut off very quickly so the engine is ready to make power, and improves its mileage and longevity by 10s of thousands of miles. So your big buck investment lasts a long time between overhauls.

Bogie

 

Ok,sounds like I can go either way,but using it is probably safer. So I guess I'll just look for a fitting and go ahead and just hook the hose up.
Im guessing I will need a 90 degree elbow so its just not going strait in the air.
What are these fittings called so I can have a easier way of finding them.

There is some confusion on where my previous temp sender was,,I actually meant the Block and Not the head. There was a plug "im pretty sure these are plugs to drain the block of coolant" but its mid motor just above the oil pan on the block. I seen on my new engine I have those drain plugs,have ports on the heads and also one on the manifold. Im guessing I could go to anyone but the manifold is probably my best bet for a accurate reading?

 

Bogie is correct in his explanation of using that bypass. You can keep the bypass plugged BUT!!! you have to remove the thermostat. It can be done, but in most cases, not recommended.

 

FWIW
Most Chevies that I've seen use the hole that is about 3 " to the right of your thermostat location on the manifold for the temp. sensor.(2nd pic)
If you try to use a 90 degree fitting in your manifold for the bypass hose, there is a good chance that it will not align the way you want it and not leak from being too loose. If you try to tighten it to stop the leak, it will be pointed in the wrong direction.
One alternative is to use the adapters/fittings in the links below. You can tighten the hose fitting pointing in the direction you want.
I'm pretty sure the hole in the manifold for the heater/bypass port is a 1/2" NPT(pipe thread).
Same goes for the hole in the water pump.
I can't tell what size your hose is. I've made a link to a 90 degree hose fitting for a 1/2" hose(-10 AN). If your hose is 5/8"(-12 AN), or 3/4"(-14 AN) use that size for the hose barb end, and do another search at Summit.
Hope this helps,
ssmonty

1/2" NPT to -10 AN Adapter:
http://www.summitracing.com/parts/sum-220047b/overview/

Female -10 AN 90 degree to -10 AN Hose Barb:
http://www.summitracing.com/parts/fra-209010-bl/overview/