To add some more information for posterity, the E70 233A increased towing capacity option included a different rear differential. Discovered this on a UK site specializing in differential rebuild kits. Back checked on RealOEM.
It also included an additional small radiator in the wheel well. This appears to be added if the car had the hot climate or the increased towing capacity option.

The European vehicles had a hot climate option which gave a larger radiator for the 4.4i. This is the same radiator standard for the 4.6iS. I can't find a hot climate radiator for the 3.0, but if I was towing I'd search more to see if it was an option.
I do see on some posted Russian sites E53s with the 233a option, but have no,t been able to determine yet what is different about it.

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2003 X5 4.6is Estoril Blue
2005 Infiniti G35X
1972 Datsun 240Z
1991 Isuzu Impulse XS Sold
1972 Fiat 850 Spyder Donated
1972 Datsun 240Z Sold
1972 Datsun 510 Sold