the black plastic air shroud fits over the bigger L shaped heat sinks. The 4x 3.5 drive midplane does not fit over the bigger heat sinks. The bigger heatsink is part number Dell YY2R8 They can be found on ebay for like $10 I run dual 150W E5-2696v4 cpus on my R730xd with those heatsinks no problemYou can also just manually control the fan speed with ipmi commandsHere is a walkthrough 
I am going to remove the mid plane on my R730XD as I don't need the drive bays and switch back to the base configuration/standard heatsinks in hopes of dropping CPU temps to make the fan noise more reasonable. My question is that there appears to be an option for some beefier 165w rated heatsinks (PN: XCYJ9 and NGC09) do these fit under the stock air shroud ( PN: Y43D5) or do I need to get a different shroud?
R730XD Midplane removal, Heatsink question