We really need a good organ builder to respond here, but in case that does not happen I'll cast my two pence worth into the pool. If that results in an organ builder or voicer replying, then this message will have served its purpose.
Yes, the replacement rank needs to be properly scaled and, yes, it obviously needs to be voiced. (I was astonished to read Vox Humana's post #3 which said no voicing was done in the case he described). But what do the terms 'properly scaled' and 'voiced' actually mean? Scaling is a strange topic in that it is precisely defined on the one hand in terms of the arithmetical progression of pipe cross-sectional areas across the rank, yet on the other its subjective aural effects in a building remain vague and ill-defined (the late and well-respected organ designer, Stephen Bicknell, suggested that "scaling is better judged as a measure of intent than of actual results"). The meaning of voicing is obvious - isn't it? Well, yes, but only if one recalls that it refers to a whole raft of things done over at least two stages of the life of a pipe. When the pipe is first made it has to be brought onto speech at the factory so it speaks properly. Then when it is put into the organ further adjustments are made as part of the tonal finishing process.
One of those adjustments relates to regulation, the process of adjusting the loudness or volume of each pipe so the rank stands comfortably within itself. The bass pipes should not dominate the mid-range for example, and the trebles should not scream. The whole rank also has to blend with the others in the instrument. Pipes are regulated by varying the flow rate of wind by adjusting their footholes (unless open-foot voicing is used, when it is done at the mouth). My personal view is that regulation is immensely important as part of tonal finishing, perhaps even more so than the nuances of timbral variation introduced by pipe scale and other types of voicing adjustment such as cutup at the mouth (which, in simple terms, varies the proportion of low to high frequencies in the sound). The late Ralph Downes also held this view, and in his book 'Baroque Tricks' he described in detail how to regulate based on the practices of the well known American voicer Anton Gottfried.
So it is at least possible that the unsatisfactory pipe ranks mentioned in previous posts could be improved merely by re-regulating them as a first step before anything more drastic (and expensive) is done. But it will need to be done by an expert organ builder.