That's a good find for that purpose. Pull the 48 off the GS crank and use that. Some guys would also get rid of the 28 and front derailleur and just run 38 + rear gears. Single front ring is getting pretty popular and around here (midwest) where you see fronts between 38-42. You'll get style points for using a crappy crank on your race bike.

Stem and bars are personal preference depending on how you ride, but I would start by copying your road position. Many ride cross entirely up on the lever hoods. I move between hoods and drops regularly. Put new brake pads on and you'll be ready.