It will fit lengthwise. To be on the safe side the maximum GPU length you can use on OptiPlex 990MT / 7010 MT is between 9.5 and 10.0 inches.  Sapphire Nitro Rx 470 4gb 230 X 126 X 41 mm = 9.055" Nitro+ RX 470 4G is 240 mm = 9.45"  
i just want to ask if Sapphire Rx 470 4gb Will fit inside my case [ Optiplex 990 ] And if it gonna work with my motherboard [ 06D7TR ]   Here is pic for the case      [IMAGE]
Optiplex 990 GPU Upgrade