Rob Butcher was kind enough to pass this along. It's courtesy of the Elias Sports Bureau...
Tonight’s game between the Reds and Giants will feature 2 players with a total of 1,335 home runs (Bonds 750, Griffey 585).
It is the highest home run total between 2 players entering a game since Cleveland played at Milwaukee on 8/1/76 and featured 1,341 homers between Frank Robinson (586) and Hank Aaron (755).
The game with the most homers between 2 players occurred on 7/17/73, when the Mets played at Atlanta. Willie Mays entered that game with 658 homers and Hank Aaron had 697 for a total of 1,355. Aaron homered in that game to bring the total to 1,356.