How to implement GST in NAV 2009 R2 in US Version?

Dear All,

There is one requirement which I need to disscuss with everyone Your early response will be appreciated?

My client is using US Version of Dynamics NAV in 2009 R2 , they have 3 company in deffrent localisation in same DB.

One company is in India version with all transactions related to taxes, Now they want to implement GST in that company.

Firstly, how much fisible it is?

And how can we proceed or suggest our client to go ahead with us?