I've started rounding up parts to do my own ABS with TC conversion. It appears it's not a problem to retrofit the Td5 and early Puma Wabco ABS to a Defender with Td5, V8 GEMS, or BMW M52 MS41. According to the 2002 Td5 Electrical Library the ABS ECU has two connections to the engine ECU. One for throttle position which is a 5 volt PWM signal, and engine speed which is two pulses per revolution. It appears both are one way communication from the engine ECU to the ABS ECU only. So as long as your ECU outputs those two signals you are golden.
The Bosch DSC system found on the late Pumas would most likely be more reliable, but it requires CAN bus communication to the engine ECU. So it would need a TDCi engine ECU or something else compatible. The Bosch system is found on lots of cars, so maybe Defenders with an LS conversion could utilize that. I don't know if you could use the Defender ABS unit or if you'd need one from a Chevy truck. It depends if the CAN bus signals are compatible.
The Defender Wabco D ECU appears to be identical to the one found on a 99+ P38 and also an early Freelander which are more common, but I don't know how difficult it would be to program for the other vehicle. You might need a chip reader attached directly to the EEPROM. The pinout listed on the Blackbox Solutions website is wrong for the Defender. It appears they copy and pasted the pinout for the Freelander version, which is slightly different. So if you need to wire it go by Land Rover's diagrams only. Two of the connectors are the same on the Disco 2 Wabco ECU. The 9 way yellow and the 15 way purple. Here are the TE/AMP part numbers.
Defender Wabco D ABS ECU connectors: They take junior power timer pins.
C0504 17 way black: 1355204-1
alternate red: 1355204-2
-secondary lock: 967634-1
C0505 9 way yellow: 1-967621-1
-secondary lock: 967631-1
C0506 15 way purple: 1-967623-1
-secondary lock: 967633-1
The Disco 2 modulator is also the same as the Defender modulator, but when it is wired for a Defender the brake pipes need to be plumbed for the Defender modulator, not what is listed on the Disco 2 modulator. It appears the main connector on the modulator is an AMP Econoseal and the single pin pump connector is a Sumitomo from Japan, but I haven't tracked down the part numbers yet. So just clip the connector pigtails off a Disco 2 at the junkyard if you don't have a Defender ABS loom.
Also, in the October issue of LRO there's a Q & A tech article about installing a new Defender ABS ECU with part # SRD000110. They state it needs coding of the VIN. I don't know what purpose that serves and I don't know what programming software you use for that. Maybe JLR SDD would do it.