I couldn't find the original thread about this, so here goes:
I finally got another The Batman GL and tried to make a custom JLU Hal.
Firstly the The Batman head fits on a pin sticking out of the neck, where the JLU head is connected to a pin that sticks into the neck hole. Because of this I had to glue Hal's head down onto the JLU body.
Secondly The Batman Hal head is too large and has a long pointy chin. I cut the chin so it would be uniform with JLU jawlines. The head is still slightly too big, but not bad, I think.
I painted the gloves and the ring and here's my Hal custom!
Here's the image, I hope it works.