you could swap the input shaft in the tcase, and it would bolt up fine. they are the same case.
4cyl is 21 spline, 6cyl is 23 spline. splitting the caser is not hard to do. might wanna put in an sye while its apart.
its possible your old 21 spline shaft in you old case was not damaged. it would go in your new 23 spline case easily.
check daveys jeeps, pirate4x4, gl4x4, craigslist, and on here to find a 21 spline case.
2005 rubicon sahara lj #592