There is no reason to change converter, 300 turbodiesel already has double friction plate lock-up clutch inside. There is nothing else differences in 722.6 converters which effects mechanical strength, althought there is three different diameters of converters.
Smallest dia. has only one friction plate, middle size and biggest dia. converters have both two plates.
300 turbodiesel has middle dia. converter, it is very good for your purposes.
There is difference in stall speeds, small converter has higher stall than big. If you tune your 300 TD you maybe need a little higher stall in your converter for best results, it is possible modify inside.
Mechanical differences between W5A330 and W5A580 are in quantity of friction plates inside transmission, it is possible modify too.
Although i think with 250-270 hp there is no need to do it.
In software adaptations, contact to mr. Mika Karala,
http://www.turbotec.com/
I hope this helps
