I put a 300tdi into a 110 with the gearbox from a 2.5 N/A diesel and the turbo is very close to the passenger footwell, but misses.
I appreciate that we are looking at a Lightweight here, but I imagine that its positioning in relation to the bulkhead must be pretty similar. As I used the 2.5 N/A LT77 gearbox, my engine is in the same position that a 200tdi would normally be, which looks to be about the same as the Series motors.
I had to modify the thin pipe that runs from the rear of the turbo to the fuel metering pump as it touched the bulkhead, you could probably get away with leaving it, but you know that it will rub through at the worst possible time. I ground the outlet off and blocked it with solder and put a T-piece on the short bit of pipe on the other side of the outlet.
If your problem is the turbo to intercooler pipe then it gets close to the footwell on the 110, but not too close.
If it is the turbo to air-cleaner pipe, the pipe from the Discovery is a tight fit, but turns through 180 degrees towards the front, the Defender pipe won't as it wants to go round the back of the engine and your engine will be 6 inches further back than a Defender. The 300tdi Discovery and Defender engines are the same, the 200's were different because the 200tdi Defender engine was 6 inches further back, roughly where yours will be if you are using a Series 3 gearbox.
If none of the above helps, it is time to break out the angle grinder and welder, like we did when we were putting V8's in Lightweights.
The pic below shows how everything fits in my 110, the small pipe, circled, has not been modified yet. The green arrows are the turbo to intercooler pipe.
