It's said that Trevor wouldn't mind... It's such a personal preference for car guys; there's one school that likes stock and others who like more modern/powerful power plants...
Personally I prefer the power, but I hot rod everything I touch. My 280i is getting a 4.0 soon, so I have been researching options recently. I will be posting soon on a new 5 speed transmission that's now a bolt-in to our engines.
Some random thoughts: The bolt in 5 speed for Euro Tasmin's was the Ford type 9 (or type N). It has been around for a while (Capri's and Sierra's), but there are a lot more available in the UK than the US.
Engine: all of the Cologne engines will bolt up (2.8, 2.9, 3.1, 4.0), even the SOHC 4.0 has the same bell housing pattern. The 3.8L is not a Cologne engine and I am sure the bolt pattern is different. The issues will be exhaust and induction.
The 2.8L in our TVR's has two exhaust ports per head, not three as in all US Cologne engines. So there's an exhaust plumbing project here.
The US never used anything but injection, but Offenhouser does make a US 2.8L version for a 2 or 4 BBL should you consider a US 2.8L. They also make an un-advertised intake for our Euro 2.8L but that costs approx $500 (the intake ports are in different locations between US and Euro 2.8L). Also, the Euro 2.8L intake (with your current injection) will not fit any of the US engines. Your choice of induction with a US engine would be either a complete US ECU/wiring loom or drive the injectors with something like a Haltech or Megasquirt - some tuning (programming) to do here. I will be doing this soon, but perhaps not soon enough for you.
I have concerns about fitting some of the newer US engines under the hood (with their stock intakes so high and off center due to the long runners coming out of the center valley and bending to the side where the plenum resides). I have not had time to measure the newer US intake heights - they look to be taller than our Plenum. I have the parts, just haven't had time to measure. I'll be fabbing my own to mimic the stock plenum so I can adjust for height...
It may be easier to rebuild the original engine. Parts are available and the engine is pretty straight forward.