Here is some added info, and you can do a search for "adding a second processor to a HP workstation" on google. HP has an ARTICLE. Here is a prior LINK.
As always, start this whole project by updating your BIOS to the latest.... it was released 4/16, and is version 3.60.
Note the orientation of the notches and triangle corner designators when you take off the original processor.... write it down, and put the new (used, cleaned) one on the same way. Be very gentle, and careful. Lift straight up and do not drop. Set back straight down, and do not drop. Those gold contact pins the processor sets against in the socket must never be damaged.
No lint..... and when you are cleaning the processor's stainless steel top cover it is best to "bed" the bottom against high quality cotton cloth folded over so there is no hard contact against the bottom resistors/diodes that stick out in the middle. Think of these processors as worth about 1200.00-1600.00 USD each, and you'll get it right. Clean the stainless cover and its edges, with slightly damp (but never drippable) fine paper towel rectangles, or cloth squares, 3 times over 'till clean, with 70 or 90% isopropyl alcohol. I even have used DNA if there is thick dried-out old thermal paste, and never let a tiny drip get under the stainless cover (it is open at one side). When the top is fully clean I use a minimally damp swipe along the bottom gold contacts, all 4 swipes, once, and make sure I leave no lint. Now you are ready to add thermal paste, and again always protect the bottom carefully.
As I have said, I prefer the Noctua thermal compound... non-conductive and has served me well on over 100 processor upgrades. You want to use a little dab..... right in the middle of the stainless cover, and about 3/32" diameter and high. I use a latex gloved finger to circle from that outward and to the edges of the cover, maybe having to change from clockwise to counter clockwise to fill in. Thin, but no so thin you can read through it. There is much yammering on how to do it..... this has worked for me always.
Setting the processor in place..... 2 fingers used, front to back, not side to side, because your fingers will fit better and you will have best final control. "Back" is the processor hold-down hinge. Good lighting..... and do not drop the processor against the exposed pins in the socket.
To attach the heatsink I use a long T handle "Torx" driver I got from McMaster.com. Not absolutely necessary.... the 4 screw heads also accept blade screwdrivers, but it is safer to use a Torx because that will keep the driver from slipping out and jamming the motherboard.
Once the processor is properly locked down in place (have a good flashlight to help you) then carefully set the cleaned heatsink atop, and screw on the 4 screws about a full turn each alternating crosswise to even out the forces as the HP article describes. Be patient, don't change the pattern, and you will finally bottom out at each of the 4. I then back off each 1/2 turn and retighten (one at a time) again crosswise, and do the final tighten-down to "gentle bottom out", as the last step. Don't loosen all 4 at once for this step. You'll get all 4 perfect this way. Probably too compulsive, but I have never had a processor install failure.
Don't forget to plug in the fan.... I guess that counts as one installation failure.
When you do your first boot you may be requested to do a restart...... If upgrading 2 processors complete one at a time to ensure function of the first before doing the second. Big time saver if your second processor happens to be bad, and that has been very rare. I think one out of over 100.