I'd keep an eye on that if I were you - there's a chance you could have reduced the cooling substantially. Stock, the fan blows air directly onto the components and it then gets pushed out the vent by pressure. Reversed, there's a chance the air will just flow over (or under as the PSU is going to be mounted to the top of the shell) the components instead of directly onto the parts then out the bottom of the case. Hot air rising and all that, you might end up with a nasty hotspot right on the PSU main board where the air isn't getting....
Instead of the parts being actively cooled by cool direct air pressure from the outside of the case, you may have a stream of warm air passing over the tallest parts only, and barely affecting the parts furthest from the fan