Just to update, I'm having much better success now, but still running into snags. Using DGIndex and MPEG2Source per Moth3r's advice after more DirectShowSource problems, and now I'm seeing that in fact it's MOSTLY progressive with a few noticeably interlaced bits (ugh), so I'm now trying TIVTC and hoping for better-looking results. So far, so good, but slow...

EDIT: Did I mention I'm trying this on a Hong Kong film? Apparently crappy telecines are kindof a thing there. Who knew? Latest script below:

loadplugin("dgdecode.dll")
loadplugin("eedi2.dll")
loadplugin("tivtc.dll")

# d2v file created from vob file by dgindex
mpeg2source("input.d2v")

# inverse telecine to reconstruct progressive frames
tfm(d2v="input.d2v")
tdecimate()

# crop top and bottom from the 4:3 frame (60px top & bottom on a perfectly centered image)
crop(0,60,0,-60)

# scale image 2x vertically, interpolating missing fields (slow)
eedi2()

# resize to anamorphic ntsc frame
spline36resize(720,480)