I can help you here.
This past weekend I flashed from Cacko 1.21b on my SL-C860 to pdaxrom and then back to Cacko again.
The installation routine is the same for the Cacko rom as it is for pdaxrom (GUI is the same, similar choices, etc.), with two exceptions:
1. You'll set a root partition for 27MB for Cacko, not 50MB as for pdaxrom. I believe it prompted me for this.
2. After you have completely flashed 1.21 and you're up and running, you will want to install the 1.21b hotfix ipkg as you would any other package.
I found it takes the Cacko rom longer to boot up on a restart than pdaxrom, so add a little patience to the mix and you should be on your way.
Bill