Quoting the instruction sheet, "
The MSD Ignition features a Gray Tach Output wire that provides a trigger signal for tachometers, a shift light or other add-on rpm activated devices. The Tach Output wire produces a 12 volt square wave signal with a 22.5° duty cycle.
Some vehicles with factory tachometers may require a Tach Adapter to operate with the MSD. For more information on Tachometers and MSD Tach Adapters, see the Tachometer Section on page 6.
If your GM vehicle has an in-line filter it may cause the tach to drop to zero on acceleration. If this occurs, bypass the filter."
Your tach probably needs the Tach Adapter.
Copper tubing will work harden from the engines' vibration and crack. This is why gauges ship with white nylon plastic tubing, not because the plastic is cheaper. An aftermarket mechanical gauge will tell you the pressure in psi, not low or high.
You need twenty or more psi at idle, and a ten psi increase for each thousand RPM above idle up until the by pass spring opens at sixty psi. Sixty psi is all the oil pressure that your engine will need to provide oil flow to the front main bearing of the engine. A higher pressure is just accelerating the wear on your timing chain and the gear on your distributor.
A High Volume oil pump (different from a high pressure pump which is made by stretching the stock oil pressure by-pass spring) is used on an engine built for high RPM operation by using a crank that has a chamfered cheek on the crank throw. The chamfer is used to keep the rods straight on the throw but has the result of narrowing the bearing and creating a internal oil leak. The high volume pump which has longer gears to increase the volume of oil displaced also puts a strain on the cam's timing chain and the distributor gear (which wears even faster if using a bronze drive gear) is used to compensate for this internal oil leak.
I use Autometer gauges, made in the USA and is a quality gauge.