If its the 400 Pontiac engine then the tach signal comes from the HEI distributor... Its the connection right next to the large red ignition wire... The temp gauge if I remember was in the head like a SBC...? Dont remember for sure...? The oil sending unit was right by the filter/housing...
Some of the Pontiac guys might have more insight or even pic`s...?
if hei it's like bumpstick said next to the red lead on the distributor cap.otherwise it's the neg.- on the coil.
temp. switch shoud be on the driverside head,many people moved it to the intake.
oil pressure will be on the back of the block.