Mike, I think you are right, it seems like its listed in One Unsafe Source...
Ok, I went and looked. I was WRONG!!. . To change from another type of anitfreeze to ELC, you first use either 6V-4511 or 4C-4611 Cleaner. Once you perform this cleaning process, you DO flush with water.
The cleaning process is an important step in eliminating cross contamination. I fully expected to wipe out the marginal H2O pump seal when I converted mine several years ago, but to date, no issues arised from cleaning/converting.