I will be draining my coolant in order to change out the engine mount and install the optional cabin heater. My question is what coolant should I put back in the engine?

This 912 ULS has been using "water" coolant and I have been told by some of the folks I bought it from it has larger radiators since it was flown in AZ most of it's life. However, the "waterless" Evans coolants looks like good stuff for a number of reasons, and I am considering it. If I go to the Evans, how much flushing will have to be done?

Advantages of Evans that I see:
Will not freeze. No boiling. Low pressure.

I'm sure there are current experiences and opinions.

Thanks much, Skot