Intalling aftermarket gauges on a chevy 250-I engine

I am trying to install some aftermarket mechanical gauges from Equus into a '73 chevy pickup with a 250 inline six engine, and I'm looking for the location to install the sensors, without having to take out the stock sensors hooked to the warning light system in the dash. I know there is some sort of plug beneath the manifold on the side of the block, but I do not know what it is for. There is also a row of plugs along the top of the cylinder heads, just above the manifold with funny flat heads that look like pinched off tubes. Any help would be greatly appreciated, thanks!

P.S, I am looking for locations for both the oil pressure sensor and the water temp sensor.  

As for oil pressure, just remove the stock oil line fitting, and put in a 'T'.  The correct term is actually a 'street T'. Normally, male thread on one end, with female on the other end & side. Pressure is pressure, and the engine won't know the difference.

Temp is a different story. You will need to find a different location for that sensor. Normally the factory one is about 1/2 way between the front of the valve cover and carburetor.  You might check out the water outlet, under the thermostat housing. On the driver's side there should be a raised boss, if it isn't tapped & plugged already.  That is a good location, since it is right in the flow path & under the thermostat.

FWIW, If you have to drill & tap it yourself, remove the housing, so you don't end up with metal shavings floating around your cooling system.

Oh, yeah. The funny, pinched off tubes is the remains of the A.I.R., or emmisions control system.
Good Luck!  
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1949 Chevy 1 1/2ton, home-built hydraulic wrecker.  Rustoleum industrial black, with flames.  Flamethrowers out 5" dual stacks.
1962 Chevy C-20, 402BB, 4-speed, 3.90 positrack. Hauls my camper.... among other things.

Thanks alot!