I'd hold the driveshaft off til after engine trans and diff are fully in. you'd hate to have it come in a hair too short or long. I've got a shop up here in Reading pa that can do a PDQ turnaround on a custom driveshaft.
http://hartmandriveshaft.com/ They do a lot of race work (the dad, Gerry H. is a long time drag and hillclimb racer, pretty sure Tim his son is running the day to day now) Just in case you're needing another source.