Pitman arm interchange, large vs. small spline

[375instroke]

I put a large sector power steering box in my '69 Charger, and used the Moog K7076 pitman arm for '73-'79 B-Body with power steering. The '65-'70 B-Body pitman arm, K780, is discontinued, and thus much more expensive now.  The K7075 pitman arm for '73-'79 B-Body with manual steering has the small spline.  If the K7076 works with the large sector box, why wouldn't the K7075 work with the small sector box?  What am I missing?

[flyinlow]