That's because your adapter isn't hub-centric. I suspect that those wheels Iachella has aren't either. Biba, I don't know how you can expect to have good braking when your Master Cylinder is leaking. I don't care if you put M3 brakes on there, it won't stop fer shiite w/leaking M/C.I have high tensile bolts held on with a aluminum plate at the front.
One problem I'm having is my wheels no longer locate on the centre of the hub.
If you're buying 15" 4x98 wheels, stick with the Alfetta hubs. Wait until the wheels show-up and see how things go. Most likely the centerbore of the wheels will be too small for your hubs, but you can fit them loosely and take some measurements. Order some QUALITY wheel adapters (spacers w/integral studs) in the thickness you want to get the look you're after with PROPER bore size on the back and a PROPER hub lip on the front - in 4x98mm.
That way you don't have to go drilling your hubs or boring-out the wheels. Too much to go wrong. Unless you just wanna look at the car while it's parked. In that case, do what these fellers did.