I need a fan for my '67 327 Chevelle. The car does have factory air, but I'll be swapping in an aftermarket unit. I measured the distance across my shroud, and it looks like a 17" is the one that would fit.
So should I go for these parts?
http://store.summitracing.com/default.asp?target=egnsearch.asp&N=4294924500+4294839058+4294838812+4294902285+4294 879472

Heavy Duty?
http://store.summitracing.com/default.asp?target=partdetail.asp&autofilter=1&part=FLX%2D5657&view=32&N=4294924500+4294839058+4294887720+4294887696

Or Standard thermal?
http://store.summitracing.com/default.asp?target=egnsearch.asp&N=4294924500+4294839058+4294887720+4294887707

Guess I'll go for the 17", with the thermal clutch.