Ok, so I got it ticketed (on LATAM ticket stock, 045) and received two booking codes - for Iberia and LATAM.
Can open booking both on LATAM and Iberia. Neither actually lists the booking class or says "business" anywhere. On LATAM I am able to select a business cabin seat, though. On Iberia seat selection is disabled, as far as I can tell. Not sure if this is because it is ticketed by another airline?