Allen,
I have a 124 with the external oil lines and assume you are running the same motor and oil line setup. Since the motor's external oil lines already use the traditional oil pan plug that is "normally" used for the temperature sender, I started looking for another place to install the sender.
I found that the oil filter adapter for the Oil Bud oil cooler is drilled and tapped for a 1/8" NPT fitting for a temperature sender. The installation of the Oil Bud cooler blocks the plug location in the oil pan, so they provided a new location on the filter adapter. You can see the sender plug location near the bottom of the three filter adapter photos on his website at
http://harleyoilcoolers.com/The sending unit location is actually at the top of the adapter when the adapter is installed on the motor.
I plan to install my old Oil Bud filter adapter this winter and install an oil temperature gauge at that time. I have an "old" Oil Bud filter adapter I took off when the 124 went in because I didn't think the Oil Bud cooler that mounts underneath the bike would clear the external lines on the 124. It may require some different fittings to allow the rubber hoses to connect to the new filter adapter, but I'll have to figure that out when I get there.
Hope this helps. It will be interesting to see if anyone else has an alternate solution...