1885-1892: Guys were hitting against pitchers who were a lot closer to the plate: In 1893, pitching distance increased from 50 feet to 60 feet 6 inches.
Prior to 1903, the pitching mound could be significantly taller than today. In 1904, height of the mound was limited to 15 inches higher than the level of the baselines - which is still 5 inches higher than today.
1920 - All freak deliveries, including the spitball, were outlawed. Prior to this, they could throw virtually anything.
1925 - The minimum home-run distance was set at 250 feet. Prior to this, the boundaries for ballparks could be whatever the home-team wanted. Today's home run hitters might take issue with that.
With rule changes over the years, there's really no way you can tell how good Mike Trout would be against a guy throwing from only 50 feet away and using the fielding equipment they had back then. Plus, he'd probably be eating a ton of crap that today is considered about as unhealthy as you can get. Then again, give "The Babe" today's conditioning and all and let him play in some of these bandboxes, 714 would only be the beginning...