I believe the 20th Bn. and the 62nd were merged into the 8th Georgia Cavalry sometime in 1864. This might help a little with the 62nd, 8th, and 20th.
Here is a site for reenactors. Sometimes the reenactors of a certain unit will have delved more intensely into a unit's history. You might try to contact them.
The 9th Georgia Cavalry was the numbered designation for the Cavalry element of Cobb's Georgia Legion. This may make research easier.