The center support bearing is secured
to the cross-member
using either a stud with an 11/16 in. nut or sometimes an 18mm nut. or it can also be sucured using a 3/8 in. bolt with a 5/8 in. bolt head and either a 15mm, 5/8", 11/16", or an 18mm nut, and GM did not stop the assembly line when they ran out of a certain nut or bolt and that is why there could be so many different ones used.
(A split drive-shaft is a balanced unit and it must be marked for proper alignment before separating the two halves or the drive shaft will no longer be in balance and will cause a vibration and early u-joint failure, and be very sure that there is a line on each half of the drive-shaft before it is separated so that the drive-shaft can be aligned re-assembled correctly
The center support bearing should be pressed off and on the drive shaft using a hydraulic press, (a machine shop usually does not charge very much to do that) and using a hammer and a drift to replace the center support bearing is not recommended however some people do replace the center support bearing that way and a lot of the time they will damage the drive shaft or center support bearing and that will only make it more difficult and time consuming to properly install the center support bearing.
(The u-joint and the axle yoke should also be marked together before the u-joint is removed from the axle yoke so that they are installed back in the same way that they came out to prevent any drive shaft vibration
To change the spark plug behind the steering shaft use a spark plug socket (a good spark plug socket will also have a provision for attaching a 5/8" or 16mm wrench to the end of the spark plug socket
) and instead of putting an extension and a ratchet on the socket, slip the socket onto the spark plug and then use the wrench to loosen the spark plug and to tighten it, but also use a length of 3/8" fuel line and push the end of the spark plug into the fuel line and then use it to start and run down the spark plugs and also to remove the spark plugs once they have been loosened.