If I understand your question correctly, I would say that the majority of these people were into the dirt track wars and ran a Pontiac engine to be different. The stroke allowed them to me a displacement rule. The 366 cranks were 3.375 stroke as you know.
I have a couple of cranks from 366 forgings that were able to be 3.5" stroke cranks and I chose to keep them that stroke. The cranks Rodney ran were even a slight bit more stroke but had poor oiling due to the bearings leaking oil around the rod journals in some thin places. One lived and one died a early death. Rodney beat the crap out of the one that lived.
Most of the cranks I sold went into circle track type vehicles. Like the ones H.B Bailey used to run. Picture attached.
https://en.wikipedia.org/wiki/H._B._Bailey
He raced for over 27 years with Tom Nell's help.
Tom V.