Back when I was drag racing, a drive line shop showed me how to install the joints. Hold a u-joint with the grease fitting at 1:30 and the caps at 12, 3, 6, and 9. You would put the transmission yoke at 12 and 6, and the driveshaft at 3 and 9. With the grease fitting at 1:30, the transmission is pushing towards 3 and nine, compressing the web with the fitting.
On a six cylinder drive train, it won't make any difference, just place them so the grease fitting has the most clearance. High horsepower guys need to worry more about it then we do.
