I am in the process of converting my FAA ATP to TC ATP.
I wrote two exams FAAAA (ATP) and FAAIA (IR), 25 questions each and you need to score 70% in each.
You need to be current in last 24 months (not exactly sure about that it might b 12 months) and they also need IPC (FAR 61.57 1&2). It doesn't matter if you did recurrent training in sim if you are flying big birds you will still need IPC.
I hope I was able to help. Please do let me know if you have any more questions will try my best to answer.
Cheers!