From the Off Road Design site:
If you have an SM465 transmission there are 3 ways to mate it to the NP203.
1: Use a factory configuration. GM mated the NP203 to the SM465 in 1973-1975 using the 10 spline output in the 465, a 10 spline female input in the NP203 and a 4.25" adapter housing between the two. This configuration was used in a wide range of GM trucks but is somewhat rare. Problems are the 10 spline connection tends to wear in the long term and it's difficult to find. Positives would be the short length and the ability to use the common 10 spline output in the transmission.
2: Use a SM465 that was originally mated to an NP208 transfer case. This 465 will have a 32 spline output shaft with a 8 3/8" adapter housing. You'll use a NP203 gearbox with a 32 spline input gear and the face of the 203 drilled and tapped with the GM round bolt pattern to match up to the factory 208 adapter housing. This works very well if you have the available length in the vehicle since the parts are commonly available and the 32 spline connection is very strong and durable.
3. Use the factory SM465 to NP203 adapter housing with ORD's new 32 spline SM465 output shaft and a 32 spline input gear in the NP203. This allows the shortest overall length with the highest strength, most durable spline connection.
