Green bearings & sure-grip center units

It depends on what sure grip you have, if you have the clutch type the thrust block can be removed by getting the pin out and the 2 pieces will pop out, a lot of times the pin is already broke and the thrust block will just fall out (make sure you find all pieces, 2 buttons and a pin). If you have the cone type the thrust block can only be removed by dis-assembly of the unit itself.

I have read some posts where some guys have not removed it and they say it worked. Most articles I have read say to remove it.

I would use an axle to align the splines BEFORE you install the center section. If you have trouble getting the axle to seat, then you can rotate it slightly while using inward pressure after the center section is installed.