it's been a while since i installed a mechanical temperature sensor.
with that said, the end bulb fitting threads into an adapter that sandwiches the bulb between the fittings, thus sealing the connection. here's where i think it gets a kink.
if i remember right, the fitting on the bulb end is STRAIGHT pipe threads, and so are the female threads in the adapter. this allows for the correct tightening of the bulb to the adapter fitting.
trying to rig up 73 adapter fittings to get to 1/8npt is going to look pretty hoaky at best, and won't be very accurate.
i would look at the water pump housing or intake manifold to see if there is a place that could be safely tapped for the gauge's fitting.
a guy could possibly fabricate a fitting from hex or square brass or aluminum stock, that could T into the inlet heater hose. it wouldn't be that hard to do, plus it would look better than a hardware store plumbing piece.