The **** is going on in here.
Yes the rims are 18x8 and 18x7.
Tires are 255/40 and 225/45 from the factory.
There is no way in hell you could ever fit 275's all the way around without having tons of issues.
Its a more simple idea to run the same size tire all the way around for cost wise and if you wanted to ATLEAST rotate the tires side to side. If the 18x7 go up front it might look a tad off with the rims being smaller by a little bit.
The reason for rotating is strictly for tire wear, it has nothing to do with an alignment, it doesnt matter if you do have a 3 year alignment thingy from firestone, that still has nothing to do with tire wear from lack of rotation. Tires on the front always wear quicker because the tires do more than just follow the leader.
And for 100 bucks thats a steal, they are worth that in scrap metal. If you want them, buy them and just run 245/45/18 all the way around. Its not going on a real gxp so buying different tire sizes in not needed.