Just a quick update - As far as the exhaust and associated pipework, I can thoroughly recommend Steve Parker's repalcement downpipe. The bodging that was involved in getting the old TD exhaust to fit to Nick's magnificent construction of a downpipe involved bits of flex pipe and bucket loads of exhaust joint paste.
The paste is really only any good for small areas etc and not much use for what we were trying to use it for. It repeatedly failed and the flex pipe kept working loose.
I've now invested in on of the conversion pipes from Steve Parker and it looks like an excellent bit of kit. It's not fitted yet (hoping to do that soon) and a new TD exhaust system, so hopefully I'll now have a fully functional sealed exhaust system that doesn't blow fumes into the battery box and thorugh there into the passenger compartment.
Apart from the exhaust issue, the only other real problem with the conversion has been the oil cooler pipes, but that's easily solved by a trip to your local branch of somewhere like Pirtek, taking your old pipes with you, and getting them to modify them slightly to fit.
Steve also does other pipework to fit the Disco 200TDi into the defender, but I can't vouch for any of that.
Steve's website can be found here and the exhaust pipe bits
are hereHappy playing!!