Easiest option is to get a conversion kit for either Marina or Ford. Most Minor places do the conversion. They are about £300-£350.
You can do it much cheaper yourself if you know what you are doing by using scrapyard parts and fabricating some bits, but the kits are by far the easiest option.
Dont forget to upgrade the rears as well, just upgrading the front brakes leaves the car standing on its nose. You may also need to consider upgrading the suspension, as extra braking puts load on the suspension.