Hey Zen,
If you are keeping the T4 cooler in lets say a DTM conversion you will hardly need any addtional cooling so I think the Volvo cooler would be good security mounted above the tranny with a thermoswitch on it. Maybe a sandwitch remote filter adapter right above the oil filter to the cooler.
I have been really impressed with the Volvo coolers. The 1/2" ID gives it amazing flow characteristics.
We need to get together anyway and I will show you how I would set the system up
Take Care,