It's a piece of piss. Simply sell the 325i and buy a 335i. If you're seriously suggesting changing the engine, 'box, the LKM, the reprogramming, the diff, the brakes, the suspension, the exhaust system and various other bits, amounting to a small fortune, I'd assume you were taking the piss.
Current: 2014 F31 320d M-Sport, Professional Media, Visibility Pack, Reversing Camera, DAB
Previous: 2013 F10 520d M-Sport, 2011 F10 520d M-Sport, 2008 320i M-Sport Coupe, 2002 325i, 2001 318i valvetronic, 1998 318i, 1996 525i, 1990 Porsche 944S2