Keep in mind that there are several models of 6 inch wheels from Cleveland and from Airframes. To be legal (and to ensure fit), they should be the model specified in your Type Certificate or equipment list, a PMA'd version of that, or STC'd for your make/model airplane. If it's not a type that was original equipment, you'll need an STC for installation.
So, you need to do a little research before you start buying used components, so you can be certain you're getting approved parts, and that they all play well together, as in brakes and wheels, proper offset, etc, etc.
MTV