Gulfscream,
The regs allow you to credit a maximum of 50 hours sim time towards a commercial certificate if it is signed off by an instructor.
B737900er,
The FAA doesn't "convert" anything above the private level. To get an ATP with the 737 type, you have to go through the TSA nonsense, pass the ATP knowledge test, complete a 737 training program and pass the ATP oral and checkride in a 737. Exactly the same steps as a domestic American commercial pilot. Many 142 Training Centers have short courses for pilots with time in type. And if the training and checking are done in a sim, no medical is required.