Converting Database from GUID to Integer Keys
Your plan sounds basically OK to me. I would proceed cautiously though - add a new int column to the tables, populate it with unique values (the ROW_NUMBER() function is handy for this kind of thing) and then change it to be the primary key and check all is ok before considering dropping the GUID cols. 

You perhaps should create a set of archive tables containing the GUID and PK for each of the tables that you can refer back to if you needed to.