742 clutch type sure grip

There is alot more than 7/16" worth of spline engagement. On a 8-3/4 sure grip there are 2 sets of splines that the axle engages into. The outer being about 7/16 wide and then the inner part. Now since you've had one spin they won't be aligned so it won't be possible to install another axle without aligning them again. It's also possible they weren't aligned in the first place and that's why it only engaged into the outer gear and that happened to you.