Ok, I won't have time to look any more at this for some time, so I'm posting the script as it is now for any who's interested in creating their own version.
It can probably be improved by someone wiser than me. ;)
Plugins used: ssiq, tivtc, eedi2 (or eedi2mt/eedi2_imp), fft3dfilter/fft3dgpu/fftw3, and of course dgindex/dgdecode. Depending on your setup you might want to try the multithreaded version of avisynth as well.
########## setup stage
SetMTMode(2,4) #Comment out if not using multithreaded avisynth
#Change paths as needed
Mpeg2Source("C:\Documents and Settings\Administrator\My Documents\downloads\Treasure Island (1990) DVD (Christian Bale, Charlton Heston)\disc1.d2v", cpu=6, cpu2="xxxxxx", iPP=true)+Mpeg2Source("C:\Documents and Settings\Administrator\My Documents\downloads\Treasure Island (1990) DVD (Christian Bale, Charlton Heston)\disc2.d2v", cpu=6, cpu2="xxxxxx", iPP=true)
SquarePixlz=true
#Set to false for dvd-ready output
#Set to true for pc-screen ready output (square pixels)
ComparePixlz=true
#true=output orginal and filtered video side by side
#false=output only filtered video
UzeGPU=false #true=use fft3dgpu instead of fft3dfilter
############ de-rainbow + ivtc
org=last
AssumeTFF()
SSIQ(7,200,true)
tfm(pp=0, slow=2, mchroma=false).tdecimate()
UzeGPU==true ? FFT3DGPU(plane=0, sigma=1.0).FFT3DGPU(plane=2, sigma=3.0) : FFT3dFilter(plane=0, sigma=1.0, ncpu=4).FFT3dFilter(plane=2, sigma=3.0, ncpu=4)
########## minimize dotcrawl/aliasing + crop/resize
Crop(12,0,-8,-0,align=true)
EEDI2().TurnRight().EEDI2().TurnLeft()
SquarePixlz==true ? Spline36Resize(640,480) : Spline36Resize(700,480).AddBorders(10,0,10,0)
fin=last
org=ComparePixlz==true ? org.tfm(pp=0, slow=2, mchroma=false).tdecimate().Crop(12,0,-8,-0,align=true) : org
org=ComparePixlz==true && SquarePixlz==true ? org.Spline36Resize(640,480) : org
org=ComparePixlz==true && SquarePixlz==false ? org.AddBorders(10,0,10,0) : org
org=ComparePixlz==false ? org : org
ComparePixlz==true ? stackhorizontal(fin, org) : fin