I've seen some trucks at shows with modern center housings and reuse old original spindles, hubs, and brakes.

In many cases that seems a step backwards to me. With the faster speed you may need/appreciate better brakes, or at least new enough brakes you can easily get parts for.
Better off swapping the whole axle complete, and the P30 axles share bolt pattern with many of these old trucks, a natural choice and good 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-