And that's why I dont have matrix based Render Code.
As much as I despise GregTech, this is one of three things you have done right with it.
Now for 1.5.1: I managed to upgrade a world from 1.4 by simply removing every adjacent block aka making machines float and removing half of the cables.
Note: This was a test, no large scale world. This might only work for a limited number.
I recommend you simply grab all your IC2 stuff and place it back down 1.5 or simply start over.