Don't know about your oil cooler lines on that transmission, but may be much easier just installing a tee on the outlet line and then you should be able to mount the probe on the tee. Did that with the old GS to mount an oil temp gauge and worked just fine for many years.
Or look for an adapter to 1/4 NPT, they do exist as per that Canadian industrial supplier, Gates 9235-12x1.25-04 is the number.
And then a little googleing takes me to that catalogue, but I am not flipping through 54 pages today. May be in there....!