Basically you need a Saw & Welder.
Your Clamps will currently look like a U with a flat bit across the top which has the 2 holes in for the bolts to clamp to.
Basically at the top of the U (So top left or top right) Cut in horizontally. Once you have done that you can then twist the flat top part round to take off the clamp from your OEM ARB.
Same on the other Clamp.
Now insert your new bush & Bar. Then just weld the bit you cut back onto the other one and all will be fine.
Point to note. Don't spend ages on it with the welder as you will melt the rubber bush. Also make sure you put some grease between the bush and the bar or it will eventually start squeaking.
I'll try and draw a pic later on if that doesn't help.
Carl