I have a manual steering chevelle and want to change to power steering. What years, parts, cars, makes, etc... are interchangeable? Or can I get any of the parts I need from the local Pick & Pull? They usually only carry later model cars. Any help would be appreciated.  

Any power steering kit for a '64-'67 Chevelle will work on your car. Since finding junkyard parts are gonna be tough, your best bet is one of the Chevelle companies like Year One and see about getting a dedicated power steering conversion kit. it'll have all new parts, and will bolt right up with no problems.