Apparently up to and including 1962, Chevrolet wasn't sure either, my 62 261 taken out of a 2 ton cabover was still in the bypass mode when it let the factory. It made it 58 years there and it is still going.

Last edited by sstock; 02/16/2020 3:39 PM.
1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration