With the brake the yoke is a “flange yoke” with a 4 bolt flange, not the spline yoke you show.
Which means you need a “companion flange” which has internal splines and the same 4 bolt pattern to match yoke, and drum may be bolted in between.

Did you not have a complete transmission with the brake on it, if so it should have all you need to swap.



1951 GMC 250 in the Project Journals
1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-