Ouch! My sympathies...
I did look briefly at the Chev conversion for mine...but too many people who know far more about Defenders warned me off....
In the end, I decided on a nice Rover V8, which will be rebuilt in 4.6 form for far less than a Chev motor, will almost bolt straight in, more power and all the torque needed, plus my gearbox and drive train will survive.... 
So far, I've yet to meet someone with a totally sorted Chev conversion who is happy with everything, and you can use a hell of a lot of petrol offroad (And gas on road) for the cost savings in the motor, and although the diesel will be worth more, it will have depreciated far more too.
Though none of the above will be making you feel better, so sorry for that, and again, you have my sympathies. Look at it this way though, if she still marries you after this, you know you'll be able to get away with murder!
Jeff
1994 300TDi Defender
2010 TDV8 RRS
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