That unit is rated for 2250, I just checked. Can I ask the obvious question, why in gods name do you need 3K pressure for? Do as you like, its your funeral as long as no one else is the one who is there when it happens, but you are asking for trouble, when you over load a system so much over spec, you are putting incredible stress on things and exceeding design limits on your valves, lines and more. Just because something can be done don't mean it is the thing to do. I'm commenting here based on experience, I have personally seen the carnage, both mechanical and bodily injury that can result from doing such.
A note for those older Vickers pumps, many of the parts for the older axial pumps are no longer available and when things go south you need to replace the entire unit on those, provided one is available. Most common ones I have heard of effected are in skid steers and swathers, but I would imagine it includes others. Seems for sure, pretty much anything with the Sperry star cast in the body for the most part are on that list.
Contracts are made to be broken, a handshake is the law of God.