The 900 series has different knuckles, hubs, and in most cases breaking systems. These out of date parts are harder to find then the more popular 800 series.
Your right I keep forgetting the mechanism that engages the splines is located on the housing. So, I will need a 900 housing and put 800 outer sections using the 800 spline size tapered up to meet the 900 spline size at the double spline section on it to keep the 800's parts availability of the ball and cup, bearings, and seals.
Thank you for the help.