20 inch rims and tires on x 4.6 setup?

[jcmoney]

question?

i have an o5 x 4.4i and would like to buy a set of 20 inch rims and tires(same set up as 4.6is stagerred 275/40/20 9.5 front and 315/35/20 10.0 rear). what would happen if i get a flat on any tire(staggered set up) and the factory full size spare is 18 inch rim. would it damage anything if i would have to put it in the rear or front until i get the tire replaced?anyhow other suggestion on a better set up(such as 295/40/20 10.0 all around, any different in ride) for my truck/what kind of rims and tires and where to buy?thanks alot in advance for the info.