The oil pressure sender is located by the oil filter and is not connected to the computer in any way. You can use a common 1/4" pipe tee to use both the new and stock gauge senders.
The water temp sender is on the driver's side of the front part of the lower intake manifold. It is not connected to the computer in any way.
The ECT (Engine Coolant Temperature) sensor is on the passenger side of the intake manifold and is normally installed in the heater supply tubing. It is a must have for the computer to calculate the correct air/fuel ratio.
If you want to keep your stock water temp gauge, here's a tip.
Alternate placement for a temp gauge sender: Use the heater feed that comes off the intake manifold. Cut the rubber hose that connects the manifold water feed to the heater and splice in a tee adapter for the temp gauge sender. Be sure to use the same water feed line as the ECT sensor. That way you will get the most accurate temp readings.
Tee adapter info:
Make a pilgrimage to your local hardware or home supply center and get some copper pipe and a tee that fits the temp gauge sender. Solder two pieces of copper pipe onto a copper pipe tee with threads in the tee part. Find the correct brass fitting to match the temp sender threads to the tee fitting.