I had a local radiator shop re-core and repair one of the tanks for my 97 Disco. I've got it all back together, but need to replace the fluids for transmission cooler, and engine coolant. Never done this before, any suggestions for a Disco Newbie?

 

Buy any of the better green or yellow coolants, mix it 50/50 with water. Consider replacing your t/stat at the same time as well as your coolant recovery bottle if you still have the old black bottle. the black ones are prone to cracking and have been replaced a few years ago with a new white bottle with better seams. You might also consider putting a bottle of Water Wetter or Purple Ice in with your coolant.
As for the tranny fluid, consider draining the rest of the fluid, not changing the filter, and adding as much Dextron as needed, may be 6 quarts or so.