The Ilford Maunal of Phorography (not sure who the current publisher is) contains lots of data on all aspects of film photography.(posted 8106 days ago)On a 35mm lens, there's usually a red dot indicating the infra red infinity. On zooms there's usually a couple of red lines.
Having said that, if you stop down a couple of stops, any focussing error will be negligible. IMO, unless you intend to use macro images then forget about the IR mark.
Try doing a test shot first and see whether I'm right. I'll beinterested to hear your experiences. BTW I use IR film in a 35mm camera occasionally.