I wish you'd ask what you mean though - do you mean the guy who actually did fighting in his own era? Then the rule changes and equipment probably baffle him and make it very difficult. If you mean if Jeffries is born in 1970, would be he be successful in 1994, the answer is obviously yes. He's quick, strong, can swat, and has a granite chin. These things don't go out of fashion.
If we’re talking about the REAL Jim Jeffries who fought from the late 19th century to the beginning of the 20th then his style, training, understanding of the rules etc probably wouldn’t transition well to most later periods. In other words, the Time Machine scenario doesn’t work for him.
He looks like one of the most limited heavyweights Ive ever seen. I think he was lucky to fight in the era he fought in. He was a big guy in an era when the best fighters of the division were as small as they would ever be and were aging. Stay safe buddy, chat soon.