Poor on both. The 4BT's sell for more and quickly for a reason.
Learn about them at www.4btswaps.com

Some folks say the 6.5 will hold together and make good power, and ocasionaly they do, but most everyone perfers the 4BT given the two choices.

Pick an engine you will be happy with, and one you will enjoy working on.

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-