The rear wheel well is tight on the GenII MINIs and moving the outboard edge of the tire outward as far as you are looking at doing may cause the tire to rub on the wheel well. The stock offset is 48mm, you are looking at 30, an 18mm change (~3\4”]. Add to that the 1/2” wider wheel (on the outboard side) and 1/4” wider tire, your tire will be about 1-1/2” further outboard than your are now. My experience comes from a set of 225-45x17 Toyo R888s on 7” wide wheels with a 40mm offset and they rubbed on bumps.

Take a look at the NAM Marketplace. I think there is someone selling a set of 8” wide wheels from a R53. An option would to be to buy those and see how they fit. If they don’t, just resell them. It will be cheaper than buying new and finding they don’t fit. Or see if you can just buy one new wheel and tire and see if that fits.

There a number of threads on this subject and you will find a number of experiences with wheel changes. When you look at them consider whether the car has had suspension mods, such as stiffer springs that will keep the wheel and tire from going up into the wheel well.

Did he say where the wheels were rubbing?

If they were rubbing in the rear, note that the R53 (Gen I MINI) has more room for the wheels than your Gen II MINI. The ones you are looking at have less offset than his, so they will be further outboard and will be more prone to rubbing

So, does this mean a change in your plans for wheels?