Audi/VW 2.5tdi inline 5 in a A6 C5

[Steve Q]

I've still not given up on the A6 and still considering options. As the title suggests I'm wondering if the Audi/VW 2.5tdi inline 5 engine could fit in my A6 C5. 

Here's the research I've done so far: 

Pros

1. I'm thinking parts would be more readily available for the 5 cylinder as it had a 17 year production run 89-06) in various cars including the A6, VW T4, VW lt and Volvo 850/V70 (known as D5252T). Whereas the V6 only had an 8 year production run in Audi A4, A6, VW Passat and Skoda superb. 
 

2. They are an older style of engine so easier to work on and they can be converted to mechanical fuel pump rather than electrical. 

3. In the A6 and VW LT they are mounted longitudinally and can mount to the 01e gearbox that's currently in my A6 as bellhousings are the same. 

4. No change in emissions class as the 2.5tdi 5 cylinder is euro 3 like the 2.5tdi V6. 

5. Proven to be a very reliable engine and can run on veg oil (WVO). 

Cons: 

1. Longer engine so might be a tight squeeze in the engine bay. C4 from bellhouse to front of viscouse fan measures around 64 cm, while the allroad seems to measure around 58. The small difference looks to be a result of the fan wich is pulled forward on the allroad.

2. Less refined as the V6 with max power output of 140bhp whereas my A6 had 155. 

3. Can't use a code reader. I5 engine uses an archaic 8 Bit ECU with no VNT provision, but can be converted to run the later T4 multivan ECU which can be flashed trough OBD and is capable to run a VNT turbo.

Unknowns: 

1. Does DVLA need to be notified of the engine swap (other than engine code) as I'm going from a 2.5tdi to a 2.5tdi? (I know insurance would). 

2. Getting the C5 instrument cluster to work (but this would be an issue with any engine swap) 

3. Would engine height be an issue? 

4. The C4 engine mounts seems not to be attached to the subframe but directly to the cars body, so I doubt if that can be done without welding.

I'd appreciate your thoughts on this 🙂