Swapped 8 3/4" pigs, now axles won't seat fully?

I recently got loaned a 489 case center section with cone-type SG and 4.10:1 gears to swap in place of my 741 case with clutch-type SG and 2.94:1 gears. After installing the new 'pig' in the axle housing I went to slide in the axle shafts and they bottom out at least an inch before the bearings are seated! I can feel the splines engage in the diff housing and it goes another inch or so then stops. All the stuff online says these should interchange but it looks like the axle shafts need to be shorter am I missing something??