I did that with my CG-5. I noticed the bottom "plug" that goes throught the hole in the tripod is tapered .040". I made the hole in the adapter accordingly but just recently realized the taper was probably just to make it easier to assemble.

This thread shows what I did and some other CNers ideas as well.

The alt/az "tang" is 6mm diameter x 1.00 pitch if you want to drill and tap your plate to use the tang from your tripod.

Looking good!

Rob