If you're going SOA.  You NEED a SYE.  Period.  Longer slip isnt the problem, the angles of your pinion/T-case yoke will not stay in alignment in a SOA application (spring wrap etc...)  
PORC has the HD SYE kit for $170 and you can get a junkyard XJ front shaft cut, balanced and rebuilt for about a $100.  Dont skimp on the drivetrain...