This is weird! You changed to a different type of pump, noise went away, but then came back. That doesn't add up to me. Do you have a mechanics stethoscope? that may help pin point the actual source of the noise, which is obviously really bad from your account.
From what I have learned from my own playing around with ps boxes and pumps, the only source I can think of for noise in the box would be the control valve. You said your box was a pro rebuild, so I'm wondering if the h/p check valve is installed correctly in the h/p circuit. That might (and I say might) cause a back flow of high pressure fluid in the pump. As for the pump itself, I'm only just getting to understand the Ford type, but from what I've seen, tolerances are very tight between the internal moving parts. If ware is too much, then moving parts will come into contact and for sure "squeal". The Lucas product may add some relief, but only a band-aid temporary fix.
As I've said many times, I'm no expert on this, but things come to mind that may or may not be the actual cause. My pump and box that I rebuilt run fine with no noise other than what would be expected.
If it's none of the above, I'm all ears and eyes to know what the noise is. Don't give up on it just yet.