I installed a temp gauge using the modified water outlet that allows the temp probe to be installed from the side. Routing is as already mentioned, follow the generator wire and through the terminal box. My repro gauge is mounted under the speedometer using one of the mounts available from the vendors.
One very annoying issue is that I cannot torque the head nut that is just below the temp probe, without draining the cooling system and removing the probe. Did I mention that this is very annoying??.
There isn't enough vertical clearance to use the thin walled craftsman socket with the probe installed and the special Snap-On S-8663-A tool won't fit between the nut and the side wall of the outlet. If I ever remove the outlet I will open that up a bit but until then...
Now not all modified outlets may have this problem, and I don't really remember where I got it as it was several years ago. But it might be worth checking out before installing a modified outlet.
See pictures.