i didn't really want a piece of this one, mainly because i end up pissing someone off, and that i don't enjoy at all.
some thoughts on your situation
the thinking of trying to match up the cells to get some sort of sets going to work
with is a good one, even if you have to break them down into 6volt strings if you have a charger that works at 6volts nominal.
forget the desulfators, and forget the edta until you have exhausted all other conventional means, i can go on about both but it really isn't necessary to do so.
your going to need to get the cells voltage up to around 15 plus volts for a while
and your going to need a decent hydrometer that is temp compensated, charge them for hours if not days until you get the specific gravity to come up on each of the cells to near what they came with, ~1260 or so. this might take many hours, and you will want to keep the water level checked and filled as necessary and keep the cell temps below about 110 degree F. if they get hot, let em rest and cool then get back after them again.
at some point you will have several cells that are going to recover just fine, so match them up in strings, there will likely be a few that are just ornery and will require more work.
those that require more work
drain the electrolyte and refill with distilled water, and connect to a charger
the specific gravity will be 1000 because it is water, and it may take several more days at 15 or 16volts to get the crytalline sulfate to break down, but over time it will as evidenced by a raise in the specific gravity, bear in mind the specific gravity will never come up to 1260 because it is mostly just water, but it will rise at some point and plateau.
once these cells have come up as far as they are going to, drain the water and refill with fresh electrolyte, and put em back on the charger for another couple hours at ~13.8 volts
then do a load test, but don't expect a new batteries performance
if after all this, you have a few cells that just don't respond, then go ahead and try your edta or desulfator or whatever poison you like, odds are nothing will bring them back to life again.
also it is fair to note that once a battery degrades to about 80% capacity fully charged of its new condition it may still look like a good deal, but the reality is the battery is on its last legs and it will start going downhill rapidly from then on. so thinking that a 1000amp/hr battery is still a heck of a buy at 80% or 800amp/hrs is flawed thinking, the batteries decline comes on rapidly soon after.
the reason i don't like edta or desulfators is based on the fact that they have never been proven to be more effective than a good equaliztion charge using the proper procedures and enough time, and there is some evidence that one can actually damage an otherwise rechargable battery by chemically altering the plates and the other doing irrepairable damage to the plates by dislodging the cystalline sulation
and allowing it to fall to the bottom where it can never be recoverted leaving the cells specific gravity lower than it should be and with the need of modifying the specific gravity with the addition of more acid. the problem being it is difficult to know how much acid to add to correct the specific gravity if you don't have the cell fully charged.
one last note, that being the copper straps you made of flattened copper pipe
if they are just straight sections and they get warm/hot they will expand in length
which places a lot of unnecessary stress on the terminal posts of the cells. this will either loosen the connections over time or worse damage either the seals/casetop or the lugs internal connections to the plates. so you may want to figure out some method for the copper to flex without stressing things if possible,
if not then i would recommend replacing them with stranded cable.
yes it is expensive, but you will have a sizable investment in those batteries time your through, no sense killing them by stressing the connections.
bob g