A-body 833 26 spline

An education, please, on the history and reason for the two different spline configurations for the 833? Was it the introduction of the 340 that brought about the 30 spline shaft?

I presume the 30 spline shaft is larger in diameter than the 26?

Will the 26 spline live with a 340 OK? My smogged out '73 came with small u-joints and rear end...but it had a 30 spline 833 in it.

What was the intended use for the 26 spline trans? 273s?

Thanks.