I dunno how you'd do it in Combustion, per-se, but here is how I would do it:
I am assuming you meen a 3:2 pulldown and not old-film (for that just hue shift it orange and drop down the saturation--for starters anyway)
I would de-interlace the footage with an interpolation, the timewarp it to 24fps (instead of 30) and then film-expand it to 30.
I have no idea if that is what you are looking for.
