300 and 400 differences
Differences off the top of my head:
Engines - probably the biggest difference since the 400 has full FADEC engines and the 200/300 doesn't. The 400 power levers have detent positions so things like take-off and go-arounds are no-brainers for engine control and power setting. The 200/300 conversely has no protection system at all, power is set simply by referring to torque vs temperature cards stuck to the controls! Torque can easily be set over 100%, and numbers of up 160% can be achieved if you're busy with something else at the time. The detent position on the 400 actually corresponds to around 130% Tq in the 200/300, which is enough to keep a couple of engineers busy for a day or so on landing.
The condition levers (prop pitch control) are almost redundant in the 400 since the computer will control prop rpm as required, so landings can be done at a reduced Np with an automatic increase for go-around power. 200/300 condition levers are cables going all the way out to the engines so you have to manually set prop rpm and even get it in sync yourself.
Speeds and limits - different flap, gear Vmo speeds etc.
200/300 are operated as Cat B, 400 as Cat C.
Different recalls - mostly due to different engine controls
Drills and Checklists are pretty close and would be simple to fix.
Flight instruments - 200/300 has EHSI and EADI but otherwise is a classic six pack gauge layout. 400 has a MFD setup with speed and altitude tapes with trend arrows either side of the AI much like a 737NG etc. Where to look for information in a hurry will therefore change between the different aircraft.
Landing technique - land with power on in the 400 whereas 200/300 you trickle it back to flight idle 1-2secs before touchdown.
Brakes - 400 has carbon brakes which need to get hot before they work, 200/300 are opposite.
So like I said in a previous post - the important differences unfortunately are the ones you need to know almost unconsciously. Anyone else on the 400 jump in here if I'm incorrect or have left things out...
So can it work - probably I reckon, but there's a lot more to it than face value suggests.