Well I spoke to some MB people on the phone today, they say it's a lot easier to do the changeover if you have a 190e 2.6 already. Although if you *did* have one, you wouldn't be putting a 3.0 in there for its marginal gains..
The main problem is that the transmissions aren't naturally compatible. Is there any sort of adapter which could be used to fit them together?(!) One person suggested the diff may also need to be changed, but I don't believe this - would I be okay with the original?
Only other thing are radiators - these are very different, and are mounted lower, but that's not a big problem.
And even got an engine price - 62,000 mile full MB service history engine, £840. How does that sound?
I've attached some pictures to help you visualize my issues, and borrowed 2phast's lovely car's pics to help show (hope that's ok!)