I have seen the GemLux install videos. One of them shows a finger like aluminum backing plate on a boat with a flat or nearly flat top. This plate can flex a little and make up for small differences. Also no rocket launchers off the back of the hardtop.
My boat has 5 rocket launchers off the back. The old rigger bases had a 12" tall base. When you looked at the boat from behind I want the riggers parallel to the rocket launcher. Purely an aesthetic issue. The GemLux Deluxe bases are low profile so its not as noticeable. GemLux sells 7.5 degree wedges. The ones I took out with my Rupp's were about 11 degrees. I'm going to make them parallel the rocket launcher and "level" them. Besides it helps satisfy my OCD!
Now the question is how to "level" them. I'm comfortable doing them either way (level across or level to tube tops in corner).
Probably get the best "fit" by putting a straight edge across when welding and doing the same when reconstructing the corners of the hardtop. The hardtop extends beyond the tubes so the lines are easy to recreate and you know where the tubes will sit.
Still have to deal with wedges. Could glass in or build them.
The new plates are 1" wider than the new rigger base footprint.