The biggest issue will most likely be in the mounting depth, rather than the diameter of the driver. I think the kappa's tend to have slightly larger magnets, which increases their mounting depth. BUT, if you fabricate a baffle that spaces the driver out a little, they should be able to work just fine. .5"-.75" MDF would most likely do the trick, as there is usually a fair amount of distance between the stock baffle and the door panel. Additionally, spacing the driver out a little will help with fitting the 6.5" driver into the factory 6x8" hole. If you're concerned about your fabrication skills, any decent car audio shop would more than likely fab up the baffles for you, for a small fee.
I'm not sure how big the Infinity crossovers are, but you could either put them behind the kickpanels or under each seat, or near your amp (if you're running one).