Yeah the heatsink air flows are in a cross + so you cannot use a wind tunnel to cover both heatsinks with a big fan.
Can you measure the length of the heatsink and see if it's 184mm long.
2x 92mm fans on the top was my next idea, depends on length of heatsink though.
yeah heatsink is 183mm long, both fans are 92mm
You should be able to stick 2x 92mm fans on top with a lower/quieter RPM in that case.