do not worry us limeys are ok with translating american
yes you really do need to get a spacer to push the wheel out slightly.
How much space do you have between the outside edge of the wheel and your wing ( fender

) as you do not want to push it out too far into the wing.
Many of the moggy dealers in the UK will sell you wheel spacers but as you are in america it might be worth getting in touch with a mini supplier in the US as they had the same 4inch / 101.8mm pcd. Most of the wheel spacers I have seen in the UK are designed to fit over a wide range of stud pcds so you might be able to get them off the shelf in a local motor factor.
or you can make your own, they are simply an aluminum plate with a big whole in the middle and four wholes to fit over the studs, and by making your own you can insure that it is a good fit and does not flop around whilst you are putting your wheels back on.