Don't go to a one piece shaft, it has two for a reason.. the length requires it.

At a drive shaft shop have each shaft checked for straightness, yokes phased correctly (welded in right to start with), and then balanced.

Grigg

•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-