I want to convert my 1968 Buick Wildcat Custom 2 Door OEM single wheel (open differential), differential to a GM 1968 OEM Positraction and use my original GM 1968 OEM gears. I need to know what to ask for when contacting junk yards, used-parts dealers, etc., for a used GM 1968 OEM positraction. Example, did the full-size GM 1968 Buick Wildcat positraction differentials come in OEM series, (which used specific gears) like the full-size General Motors 1957-1964 Pontiac/Oldsmobile positractions? I was old some years that the GM 1968 Buick Wildcat Positraction is the same as the GM 1968 Electra Positraction. Are there other GM models and what GM years that would fit with my GM 1968 OEM gears? What are the identifying numbers, letters, symbols, features, methods to identify the used applicable GM OEM Positraction for 1968 that would fit my 1968 OEM gears? What is the information source and other contact methods, ex. names and/or phone numbers. What are some possible sources for used applicable GM OEM 1968 Positractions or other models and years that would fit my 1968 GM OEM gears.