Well,
As you are talking about GCAT i presume your friend currently has no 737 rating. Therefore as he is in the same boat as me i presume the selection procedure he will be going through will be the same.
As you stated an interview with ryanir, and then he/she can expect another interview but with GCAT itself. This is supposed to be the more technical of the two interviews but in my case ended up being the debrief and informal chat following the sim ride. The sim ride is then just a simple t/o, SID and STAR, most likely all at the same airfield. This was done in the B737-300 sim at Gatwick. No asymmetric.
Hope that puts your friends mind at ease, this was what i faced but then again things might be different for them.