IndyMac Bancorp, one of the highest-ranking thrifts in the mortgage market, has even loftier aspirations: to be a top six lender by 2010. Officials revealed that goal to investors at recent conferences sponsored by JMP Securities and investment bank Raymond James. Inside Mortgage Finance, an affiliated publication, ranks IndyMac as the 10th largest lender in 2005, with $60.77 billion in originations. To break into the top six, the thrift plans to stick with its “best…