I just went through this subject with the machine shop that did some work for me during the rebuild of my 261.I also changed to full flow oil filter.
While he had my block he made the change for me by moving the diverter in 5/8".
The guy seemed very astute on the 261 and did a great job for me.He once raced these engines and was talking way over my head about performance and modifications.
Hobert
