I've never converted to the metric system in my mind yet so I'm not sure exactly how wide 1MM is, that being said are you sure the rims are offset or inset 1MM? Inset would locate the rim center closer to the drive shaft and offset would move it away I have a 1966 Dodge Cornet Deluxe that I put a narrowed Dana 60 in and moved te rear leaf springs into the rear sub frames for more tire clearances, I put a set of 8x15 inch wide rims and a set of 275x60x15 tires on those rims. I did have the front fenderwells stretched, move forward, three inches and I used a set of the Mopar SS leaf spring that moved the rear end forward two inches also I should have measured better with those tires and rims before having the rear end narrowed, the front of the tires are really close to the front inner sides of the stock wheel tubs I ended up having to use a .500 inch wheel spacer on the rear end to get more room so the tires wouldn't touch to start with You may want to see if you can borrow, maybe give the wheel shop a refundable deposit to take two of the rims home and see if they fit with no tires on them to start with
Take time now to make sure what you end up with fits IHTHs