What's your source?
A DVD source with well-behaved pulldown is probably best handled using the "force film" option in DGIndex.
Any other source, if the pattern is constant, can be IVTCed very quickly by
doubleweave()
pulldown(a,b) # a and b need to be chosen manually.
Strange/inconsistent pulldown patterns may need to be handled by an automatic AVISynth filter such as Decomb or TIVTC, but this method is obviously slower because of the field matching algorithms in use.
You do not need assumefps(23.976), because the 29.97 fps video is decimated by 4/5 during IVTC to get 23.976.