yes they are identical cars but you must do a complete swap (engine ECU as well) Kyle
Not easily. The 940 engine is a 4 cylinder rear wheel drive that is oriented front to back. The 850 engine is a transverse 5 cylinder front wheel drive. The transmission/transaxle in the two are very different.
The seats from a Volvo 850 will not be able to properly fit into a Volve s40. This is because the vehicles have different body types and do not mesh with one another.
IDK if it will fit, but it did I dont think you could even get that turbo spooled up on a 3.9L engine.
BOTH - 21" (inches)
No, a turbocharger must be appropriately sized for the engine.
No, only a certain range(size) of turbo will work(efficiently) for a 1.6 diesel at the rpm range, boost throttle response you want. Link below is to one of the best turbo calculators, IMHO.
If you have a Volvo roiginal radio, it is likely to be produced by Alpine. Depending on your radio, different Alpine changers may fit.
citroen/peugeot made by ford
Yes. However it's not that easy due to the turbo versions electronics (if it's a 700 series turbo your after). But fully possible and has been done several times.
Yes. Starter/Bellhousing issues
The sensors are not there I dont think. You will have to get them from a Turbo Diesel engine and prob fit the sensors. ALOT OF HASSLE! Its not worth it. You could buy a turbo diesel 205 lump and fit that with the wiring loom? Still lots of work. I fitted the engine but not the loom and dont mind that I dont have a rev counter.