I went with a NASCAR driveshaft which is 4" diameter for use with my TKO 600 and it has the huge 1350 series front C6 yoke and I was able to give the length needed to the inch and they stocked for around $130.00. That was last year. His Ebay store is listed below and he currently has them for $94.00 shipped and they are in 1" increments. These things handle 1000 hp plus!!
http://stores.ebay.com/MuscleMotorSports-Store