Driveshaft length

74 valiant with manual transmission, 318 or 360, 8.75 rear 48.96 inches center to center. Use this as a double check, measure as pntastar69 says, sitting full weight on the tires. I would slam the yoke all the way in measure then subtract, that way you only have one measurement and one chance for error. Triple check with you driveshaft shop. Everything makes a difference, you might as well get your driveshaft perfect for your setup.