Look at number 8 in the picture.

Ok, then take another look at the pic and the game and see if by taking off the globe on top the whole assy can be dropped through the bottom. See item 9, 11 and 12. Also I just saw this pic on the net, it looks like the planet rod will pull straight out.

s-l1600 (resized).jpg

If I remember correctly, after the light assembly shaft is removed(I think there's a cotter pin in the bottom that holds it stationary, also there might be an issue with the connectors not pulling thru but the male or female pins can be delicately removed from the connector. Someone just cut the wires and repaired in the pic as an alternative)
After the light assembly shaft is out all the nuts can be reached for loosening. then the whole remaining rotational shaft and motor assembly slips out from below.

Ya know, if it's too hard, you can remove the plastic panels from under the playfield that surround the planet and remove the entire assembly as a unit so it is easier to work on.

What you don't want to do is try to turn that large top nut without holding the lower one with a wrench.