I've got one on the go right now
I have a 156 GTA 3.2 engine with 6 speed box being installed in one mine, being done by Nick Troth of P1X 2000. I took a ride in his 3 litre V6 car and I just had to have one. All I can say is it takes a lot of surgery and is quite expensive!
Sorry for grainy image, it's from Nick's mobile phone.
Some specs:
Alfa 156 GTA 3.2 V6 240 bhp (probably a bit more as I'm removing the Motronic afm)
Alfa 6 speed gearbox, cable change
Megasquirt II injection and ignition
AVO monotube coilovers all round
AP 4 pot calipers, 330x30 front discs
Girling calipers, 284x22 rear discs
Alfa 164 brake master cylinder
OZ Mito 3 piece wheels, 8x17 front, 9.5x17 rear
Seicento 35 litre fuel tank in front
Scirocco radiator, exhausting up through bonnet vents
Eurosport/Dallara replica bodywork
Colour probably 1300 lime green (undecided)