Finding good data of the financial side from MLB's past years is difficult, since the information is rarely made public to any great degree.
The best sites I've found with data are:
http://www.bizofbaseball.com/
http://www.super70s.com/Baseball/Tea...nd/Financials/
http://www.rodneyfort.com/SportsData/BizFrame.htm
In terms of finances in OOTP, one must remember that, while the game models reasonably well the income side of the ledger, it does not model all the costs on the expense side of the ledger. For an OOTP team, the only expenses it has are its players and coaches. That's it. A real club, of course, has a lot more things to spend its money on, such as spring training, travel, taxes, front office staff, stadium upkeep, minor league affiliates, just to name a few. A real-world major league club only spends roughly half its revenue on its players and coaches.
Thus, in OOTP, if you want salaries to approximate those typical in a certain era, you must use settings for club income which are below the actual historical values for that historical era. That means either using lower ticket prices, lower attendance, lower media contracts, or some combination of the three, in order to compensate for the expenses that an OOTP ballclub doesn't have.