Hello MTInter   You can use slot 1 if it is available. For slot 3 you need this riser and second processor Riser Pn#5NV48 - ASSY,MECH,R2C,1X16,LP,R45/6XS ASSY Mechanical, 3, 1X16 Slots, Low Profile
Hi    We have a Dell HBA 355E adapter which we need to install it in addition to an R450. I believe we require a riser for this. Can you please advise the part no that we need to order?   Thanks Matthew 
additional HBA to Poweredge R450