quest,
As the holder of a foreign ATP, in order to get a FAA ATP you have to hold a FAA medical, pass the knowledge (written) test and pass the checkride. Because you hold an Indian HS125 type and ask about an oral and sim, I'm guessing you want a HS125 type on your FAA ATP. FAR 61.157(b) gives guidance on type ratings at the ATP level and says you need training records and an instructor's sign off to take the type ride. So you will need to go through some training program before you take the ATP checkride if you want to do it in a HS125 sim.