These were a factory option in some of the later big blocks that were high performance. I plan to go with a quiet gear drive. I just like the reliabilty of the gear drive systems...I think the chevy inline 6 like my 230ci is a good example. No chain to stretch also. I picked up a chevy big block engine book and it talks about the factory recommendation of drilling these holes to provide more oiling to the gear thrust face. Were only talking about a 1/32" hole. They use whats called a wire bit to drill it. I haven't talked to my machinest yet, but I was just curious as to the population of gearheads.
