Does a 455 olds require a 5 degree down angle when installing and is that measured at the driveshaft?

 

The engine doesn't "require" an angle. If this is a custom installation, you typically want the carb flange to be parallel to the ground and the output shaft of the trans to be parallel to the pinion on the rear axle.

 

thank you Joe that helps me

 

3 to 5* is the recommended engine angle, as long as the rear end is set up correctly, that is 3 to 5* pointing upward.