^Well aren't those coolers tapped into the lower radiator hose? It would seem to make sense that the coolant in the lower hose is much cooler than the coolant either in the engine or in the radiator since it has already had the heat pulled from it and is now returning to the engine and would therefore be capable of sufficiently cooling the engine oil as well. Just thinking out loud.
The coolant on the passenger side of the radiator is the hot side, then it travels across the center core of the radiator to the 'cool' side for return to the engine. That is why the tranny cooler is in the tank on that side.
I did some reading on it out of curiousity today, and it seems the water to oil cooler has 2 benefits:
1: It brings the oil temp up to operating temp quicker. The water in the engine heats up far quicker than the oil. Everything I am reading says that it benefits the oil to heat up quick.
2: It then cools the oil, and keeps it the same temp as the water, which is the goal. Without the cooler, the oil can reach temps several degrees higher than the water, at least that is what I am reading.
I just googled it worded a few different ways, and I got discussions from tuner forums to Z06 Vette forums (many late Vettes apparently had/have these coolers, and the haves were debating the have nots)
All that said, I still don't think I would use the tranny cooler for this purpose, personally...
I don't think the diameter of the tranny line is big enough to flow the volume necessary.
I would lean towards a P/S cooler myself, and then use something like the truck cooler on my oil.
Side note: I just realized, I also have one of these Ford style coolers mounted to the engine on one of my concrete saws. I put it on my 65hp air cooled Wisconsin 4 cylinder engine. The water to cool the diamond blade now travels through the oil cooler first.