Ok, here's my solution.
Now, on my car, have -6 AN transmission cooler lines running up to the front of the car because I added an extra cooler, and there's a bit of rubber hose in the front connecting the radiator cooler to the external cooler, with the braided AN stuff running to/from the transmission.
So, this setup hooks into that. If you have the steel lines, you can just cut/section them, then use the compression fittings included with the manifold (things with the plastic caps on them) to splice the manifold into the fluid path.
Here's the parts list:
Autometer 2286 Manifold
Russell 66040 AN-6 male to 1/4" NPT male fitting
Russell 661580 bushing, 1/2" NPT male to 3/8" NPT female
Russell 661570 bushing, 3/8" NPT male to 1/4" NPT female
Generic 1/4" NPT threaded sensor
1/4" NPT male to 3/8" ID hose barb adapter
1/4" stainless steel bolts, washers, and lock washers
The two bushings are because the temp sensor I had was 1/4" NPT, so I had to step down the 1/2" NPT hole in the manifold. Adjust the bushing adapters to whatever you've got.
When you hang the assembled manifold, make sure the sensor is DOWN. If you mount it sensor up, there will be an air bubble trapped around the sensor and your readings will be poop. Use sealant. I used PTFE paste. Stuff works great.
Here's the finished product. The line from the transmission to the radiator cooler inlet comes in the AN-6 on the right side, and the rubber line going to the cooler connection goes on the hose barb.