I know this is an old thread, but I stumbled upon it when I couldn't find a Radiator (for a sensible price) for my Mk4 2.3 tina. Based on the above I went ahead and bought a Radiator for a 2.7 TX1 Taxi. I was really surprised that it doesn't fit easily at all. List of jobs needed:
1. Create brackets. I expected this as its mentioned above
2. Re-locate Power steering cooler. This has to be moved as TX1 Radiator is larger than original
3. Lower fuel return pipe. Again this gets in the way of the new Radiator
4. Modify/source new hoses. This was also mentioned above
5. Fit electronic fan/switch. This was the most annoying issue. The new Radiator is 3 core instead of the mk4's original twin core and therefore takes up more room preventing re-use of the old fan.
I'm not sure how the others above overcame these issues, but wanted to mention it here. Had I known about the need to buy and fit an electronic fan it would of put me off going this route because it adds £40 to the cost and really makes the car more modified than I wanted it to be. New Radiators for mk 4/5 v6 are available from Germany but they are £250. My car needed several other jobs as well, so I was trying to keep the costs down as much as possible.