The diameter difference isn't a big deal, its minor, I wouldn't worry about it. You put the foams in and then glue, I recommend you watching tire glueing videos on here because they will come off with brushless power pretty easily. I think within the past two pages or so on this thread I posted some information on how to remove and prepare tires and wheels for glueing. Its good to wash everything with simple green first, the glue will hold a lot better. Also roughening the surface up with a dremel wire wheel or sandpaper helps, too.
You will need a vent, though, when it gets hot they will balloon if you glue things too well.
You can put holes in the wheels but if you drive in loose dirt they will fill the wheels and mess things up. The best thing to do is put a few holes in the tire tread with a leather punch.
Last edited by nitro-rob; 03-11-2014 at 12:26 PM.