Because the tranny cooler lines are above the transmission, you won't get much drippage. I usually tie a sandwich baggie over the end of the line to catch what drips there are.

If you believe in your heart of hearts that there was intermixing of coolant and tranny fluid (it does happen), you will probably want to flush and fill with the cheapest fluid that meets spec. Drive it a few weeks and flush/fill with a brand that you trust. If you can replace a radiator, you can flush the transmission by the method in the 700/900 FAQ. The hardest step is getting the cooler lines off the radiator...you'll already be there.

Also flush the coolant system when changing the radiator. If there was tranny fluid in your coolant, you'll want to get all of it out.

Good luck with the project.