**UPDATE** I have a 280ZX I'm not using, so I pulled its coolant inlet port off and installed it on the 240Z. I've learned that the later L-series engines have a threaded inlet port. I've plugged it with a 1/2" pipe plug and installed the Lower Radiator hose.
Note: If you choose to do what I did, the lower radiator inlet port from my '81 280ZX is slightly pointed more engine-side than the original 240Z port. So watch out for the lower radiator hose touching your alternator. What I did to fix this problem was to twist the lower radiator hose at the bottom of the radiator to clear the alternator. Well, it doesn't completely clear the alternator, but as long as it's not touching the fan blades, I'm fine with that.
** I've completed plugging my cooling system. Thanks, HybridZ. Your input was very helpful. **
First off, I'd like to mention that I removed my heater core. So no coolant flows through the interior. I'm trying to bypass that and apparently there are two popular alternatives to that: "looping" or plugging. I'm convinced that plugging the cylinder head outlet is the most logical way to go, since all that looping does is move cold water from around the left side of the block/cylinder head and back into the water pump inlet. Since I've deleted the heater core, the cylinder head coolant outlet is no longer necessary.
Also, my engine is stock. I found a popular thread pertaining to cooling on L-series motors for racing purposes, but I feel that for stock motors that advice doesn't apply.
With that said, I'm having a tough time searching on hybridz advice on how others deleted flow to the second inlet. Maybe it's so easy to do, that it goes without saying, but I'd like to know what people who have plugged their systems have done in order to delete their loop.
This is what I'm going to do:
Thermostat housing => intake manifold plug
Intake manifold plugs (front and rear)
Cylinder head coolant outlet plug by the #6 cylinder
And here is where I'm stuck. The water pump inlet is branched into two, one for the lower radiator hose and one for the heater core hose.
Should I tap the second one and then plug it with an npt plug?