I honestly don't think they will even physically mount to the rim. Sell your tires and save for the correct sizes. It will look alot better and be safer to boot.
Well you could drive on the old rims & tires till they wear out, then replace them with your 10.5's and new tires or just bite the bullet and buy new tires and use those new wheels you bought??
I would not do it. I have 275/40 on my 10.5 bullitts and it is in my opinion too small. My next tire will be 315/35. I would just wait or just sell your old tires.
Actually they will fit. That is how drift racers set up their rims. So you can do some really cool driving with that. Post some cool videos when you're done.