"Mounting bracket Xmm" will be the width of the top part of the hub that slips into the bracket on the bottom of the front shock. Its narrower on Twinsparks, wider on V6s.
Swaybar mounting is for cars where the front antiroll bar has droplinks to attach it to the shock body. Some GTVs have droplinks which attach the front antiroll bar to the lower arms instead. I can't remember which yours will have but it wouldn't hurt to buy the set with the swaybar mounting attached even if it turned out you didn't need it.