In '81, I guess Chevy started putting an NP208 T-Case. This case has a 27-32 spine shaft. They used an adapter from the factory to mate this case to a TH400. My question is.........can I take the 21 spline shaft out of my NP231 and sub in the 27-32 spline shaft. This will enable me to use the factory adapter on my Jeep conversion and save me some bucks.

In '81, they did switch over to the 208 t-case, BUT, unfortunately, '81 and '82 cases that were behind the 465 were 10 spline.

In '83 they were made to 32 spline. So, if you find an '83 or newer 208 behind the 465, it will have the 32 splines and able to mate to the TH400 tranny.

As for the 231 t-case, I have no clue whether the parts from another will interchange or not.

I'm not all that familiar with the 208 but I think it has a different reduction ratio than the 231. The 231/241 have a 2.72 reduction. I seem to remember the 208 having something in the 2:50 range.

If you are trying to match the correct spline on the 231, you can swap in a 27 or 32 spline shaft from an NP241. The 32 spline shafts are hard to come by but the 27 spline shafts are pretty abundant. The 400 used a 32 spline shaft as did the 4L80E, NV4500. The 700R4 and the 4L60E used the 27 spline shaft.

National Drivetrain in Chicago can get you new or used shafts and they are a direct replacement for the 21/23 spline shaft in your 231. You may want to upgrade to the 6 planet carrier from the 241 at the same time if you're running a SBC. Only one thing to be careful of on the 32 spline shaft. Some 241HD's came with a different front bearing. If you get a 32 spline shaft from a 241HD you will also need to get the front bearing with it.

208's have a 2.62 low range. ;)