What is surprising in converting from one type to another is the necessity of going back to first principles. Attitude/Power/Trim/Scan. The view out the front is different, ie the horizon is in a different place. The control response is different (or the wrong way if converting to clockwise rotation). Unlearning is as difficult as learning. Instrument panels have the guages in different places, sometimes even on the same type, so scanning for the info takes longer. Glass presentations are grand if only there was commonality in presentation. Time spent sitting in the cockpit (in absence of simulators), practicing all the drills, preferably with a really knowledge person is never wasted, otherwise when you are in the air you will be neglecting what's going on outside while you are searching for the right guage or switch.
A certain North Sea company (going back a bit) picked up a type from another company in a takeover in which all the non flight instruments and switchery were in totally different positions. It was a reminder of how much this slowed down ones cockpit scan (ask me how I know).