All of the fights in the game take place in the Las Vegas Hilton casino in the North American version. There are also advertising banners for HBO visible during fights that are not available in the Japanese version.
In the North American version, the blood is colored red while the Japanese version uses sweat instead. This is contrary to Nintendo's then-current censorship policy that blood should never be used in their games.
Source: Wikipedia, "Boxing Legends of the Ring", available under the CC-BY-SA License.