I'm assuming you found the ACS to ISE migration tool? Since you self referenced I'll just make a quick note for when people search google and end up here.
Each version of ISE has a specific ACS to ISE migration tool to aid in the move. It's not perfect but it saves considerable time in large deployment. When you use the tool you have to go through all of the policy sets and clean up the logic as the tool duplicates a lot of conditions. You can find the tool in each ISE version download section on cisco.com software search, ex. it's nested within ISE 2.4, another is nested within ISE 2.6.
