Actually haven't a clue, never been up to those pressures.... You would certainly need to lean on the hammer spring quite a bit to be able to utilize a 3000 psi fill without the velocity dropping like a stone because of valve lock.... It is POSSIBLE you might get there by shimming the stock spring to the maximum, maybe combined with shortening the back of the hammer and the spring guide.... but I wouldn't guarantee it.... I had about 1/8" more preload available on the hammer spring than what I needed for 1600 psi on the last QB I did.... I have no idea if that would be enough for 3000 psi or not....
If you can't get there with a stock hammer spring and shimming (or using an RVA) then you would have to find a stronger spring.... The only one I have found so far that will fit is a 0.360" OD x 0.059" wire Trakar spring and it is too big to fit in a stock hammer.... Since they are hardened, now you are into making a new hammer to fit the bigger spring.... and on it goes....
As far as the safety of the valve attachment system, I would have to do the math on that to determine the safety margin (if any) at 3000 psi....
Bob