You could take the easy way out an feed it through HiCon32.
Profile 20* - SDTV(us) 60Hz to 120Hz (720x480/60i to 720x480/120p)
* assuming NTSC
You can use MakeAVIS (from ffvfw) to get your avs script into HiCon32 as an avi. The conversion takes a considerable amount of time for what's being done, but you'll be able to see whether or not it's worth it in the future, or if it's something you save for those rare impossible sources.
I prefer to use YATTA for the pleasures of manual IVTC, but that's just my opinion.
Hmmm... am I the only person in the world with a setup that will NOT run SmartDecimate?
/me goes back to trying to get SmartDecimate to actually work again