B6 Passat - swap 103TDi motor for 125TDi vs chip/etc? Possible or nuts?

[yetizilla]

I have a '07 Passat 3C 103TDi and a '08 Golf MkV GT Sport 125TDi both with 6spd DSG (Golf fitted with flappy-paddles).

Engines are quite different with the 103TDi almost aggressively economical in combo with the DSG and the 125TDi much more peppy around town though would be on par I imagine in economy if not for the fuel tank sizes. On long trips and my 1hr commute to/from work the comfy Passat is the car I'd rather be in and though 103kw is sufficient, having more cannot mean less enjoyment

Not knowing about the existence of a 125kw motor when buying the Passat (along with the injector failure feature on the BKP series) it recently got me thinking having driven the wife's Golf a bit more recently, rather than chip/tune the Passat, can the 125TDi motors (from next year model onwards) be transplanted? The cost of an engine is similar though labour is the unknown quantity, especially if its a pain...

What are the difference between these motors too giving the extra power/torque - turbocharger, injectors/injection type/pressure, just maps or a combo?

Has anyone done this, whats the difficulty/problems/gotchas; and do all of the 125TDi's have the DPF? Or am I just nuts for even considering, and should focus on component upgrades?

Haven't been able to find much on this so eager to hear.

Thanks

[kamold]

Why not just get a tune on the 103TDI?
MUCH easier and cheaper and will get you similar output to stock 125, at least on paper.