Hi Cen Racing......
I have just replace the GS087-90 on my cen and i found it terribly difficult to align the gears. It is almost impossible to get the things square with each other.
SO i did a little design of my own being an engineer myself.
What i did was remove the motor completly from the frame. I then scored parallel lines into the engine plate GS041 1mm apart from the the Chassis plate GS037. I then drilled and tapped 2 M4 holes through the side of the Chassis plate equal distance to the far end of the edges to the motor block support GS071.
Now all i need to do is replace the motor and softly tighten down the engine Not to much other wise the block will not move. I then put 2 M4 screws in the adjustment holes.
Now using the lines for reference i turn the screws equally pushing the engine block closer and closer into each other giving me a perfect alignment for the gears GS087-90. By checking the block position against the lines i can be sure that everything is parallel. Once the gears are in the correct position i just screw the block down secure and remove the screws. Harder than it does not have to be
This might be something for the future you might want to add to improve the usability of the truck during repairs and upgrades.