Hi, I found a butterfly riser card compatible with the R540 from the spare parts system. But I must say that I cannot see the part number you need to make the configuration you want. It would be correct to look at the R540 with access to a riser configuration matrix. Usually, the sales team has such matrix sheets. I looked a lot, but I found topics like Expansion card installation guidelines that you have already seen. I can't be 100% sure of the part codes needed for these. I don't want to mislead. I would contact to local sales team. 
G'Day all, We have two del Servers Dell R540 and T440. On both we installed New Dell x710 Network Cards. Both Network Cards working fine on T440, but on R540 no Card is detected in iDRAC9 under System -> section PCIe-card. in PCIe Slot 4 is EMPTY (Slot4 is needed its 16lane i need for the fibre card 8lane / Slot 5&6 are only 4 Lane)   Special is i see a network card under iDRAC9 under System -> section Network Device -> here is a NIC Slot4 reported a X710 Network card. i see the link is up and all.. Both cards are not working on R540 but works fine on T440 also are visible on T440 under PCIe-cards. on R540 no operation system or Diagnose Tools see the card. Not visible in Lifecycle manager or Dell support DVD with lspci command. i hope this is just a bios problem?  both Dell servers are on same Bios version also DRAC version. hope someone has an idea? thank you very much.  
Dell R540 Server and Drac not detect the New Dell x710 Network Card