Re: Fiat 20v turbo engine change
I'll have a go although I haven't gone near this job.
I reckon you should take the engine and box from the Coupe together with ECU, all of the airboxes, rads, intercooler, ac pump, etc.
Keep the steering/suspension on the 156.
You will possibly need mounts or a subframe from a 156 2.4 JTD.
On the Coupe only one mount meets the subframe- the one under/behind the engine. I think I've seen one in a similar position on a Twinspark 145 Cloverleaf.
There are 2 that mate with the inner wing and a reaction strut.
Driveshafts I'm not sure about. Maybe one or other will fit or you may need to cobble something together. The Viscodrive on the Coupe may mean that you can't get something of the right length to go in a 156.
Good luck with it. I have some photos of Coupe 20v/T engine mounts if they help at all.