BENGALURU, Sept 23 (Reuters) - U.S. private equity firm KKR & Co Inc will invest 55.50 billion rupees ($755.09 million) in Reliance Industries Ltd’s retail arm, giving the unit a pre-money valuation of 4.21 trillion rupees, the Indian conglomerate said on Wednesday. KKR"s investment will translate to a 1.28% stake in Retail Ventures Ltd, according to Reliance. (reut.rs/3hWbyAc) ($1 = 73.5010 Indian rupees) (Reporting by Philip George in Bengaluru; Editing by Shounak Dasgupta)