I don't have much information about the cabinets for you. But I can tell you what one is worth just for the cab.
About $350. That is what the only Duramold cabinet to show up at auction in the last few years sold for. It was converted to Shinobi. Another Duramold Shinobi (maybe the same one?) was advertised for $350 about a year and a half ago (in a different state).
A Blaster Duramold with a boardset problem brought $500 at an auction in 99 (but that was when the home arcade scene was just taking off).
Also. The most common Duramold game is Blaster (black) , followed by Bubbles (Blue). There are a scant few Sinistars as well (they were probably test pieces, and were also black). Red duramolds are widely rumored, but no one can ever actually seem to produce one (they are usually rumored to be either Sinistar or Inferno).
Also, don't forget the rare Blaster caberet duramold.
Couldn't you buy a 6 foot tall, 24" diameter plastic pipe and cut your own Duramold out of it? I am sure plastic pipe that guage must exist for some commercial applications.
Also. they may not have needed to be counterweighted. The piece of wood with the isolation transformer and power supply in the bottom of most cabs rivals the monitor in weight. Now add in the coin door, coin enclosure, and boards (Williams games had several). It should be balanced. Really no different than a wood cabinet as far as weight distribution goes.