When talking about the 1960 optional 261 you are beginning to travel down the river stix (spelling, don't believe that stuff). the optional 261 in 1960 had for both the automatic and standard shift a #57 metering jet. In my opinion the 57 is a good all round metering jet. Unless you have a 261 from a bus that was governor equipped from factory then you need a #42 jet. This is a Rochester BC carb. If there is any evidence of a governor attached throw it away and go with your exiting BC. Most governor's at the time kept the speed at 45 mph. I'm a Rochester/Carter Nazi so you may need advice from tclederman or hotrodlincoln. There is a gold mine of folks on this web-site that have pretty much seen it all. A plane old Model "B" with a choke pull off is my preference on all the oldies. Stuck in my ways Doc.