Best practice for developing for iphone and ipad3 simultaneously?

I am working on an app that has similar functionality on all devices, but completely different GUI elements for iphone, ipad and ipad 3.

How can I structure my code so the ipad 3 GUI assets are not included in my iphone build? Right now I am simply using an if statement to determine the screen resolution and then adjusting the GUI accordingly but this wont work when it comes time to publish the app.

Should I split my app up? I would really rather avoid fragmenting everything like that but I havent found any solid advice anywhere else.

Thanks

Why wouldn’t it work? You can check Screen.width and such after the publishing, too. Of course the different assets are included, but they have to be, if you’re not willing to do separate builds (split it, as you put it). How much does your different assets take up space? If it’s only few megabytes, I’d say it’s acceptable overhead for not needing to publish two apps.