Ok Just about anyone who has posted about upgrading a mini c to brushless needs to see this vid that another guy did that shows exactly what he did to his mini c. It will give you an idea as to the space or lack thereof that you are dealing with. [link]http://www.rcuvideos.com/video/How-to-convert-Your-Proboat-Min[/link]
The Rio Ep is fairly new so not much known yet, other than as cornelp said it is bigger so would be able to maybe not be too much concerned with spacing. Good luck which ever way you go.