The tow bracket and bolts are pretty substantial. After all, the nose weight of a 3.5 ton trailer is likely to be more than a lightweight motorcycle. You're not exactly carrying a Honda Gold Wing. So spacing the tow ball out an inch or two on a metal block isn't going to cause anything to fail I wouldn't have thought, even with the weight of the bike.
 
I've got one like this
http://www.extreme4x4.co.uk/Store/Rear-Wheel-Carriers/rear-wheel-carriers-1
It's handy as it has a place to put the Hi Lift jack too. It's galvanised under the black paint.
That is what I have on mine, although I got it second hand about 8 year ago, so it is from the era when xtreme 4x4 was scorpion racing. I would say that the highlift bracket only fits a geniune highlift. the base plate is too samll for my highlift. it is also only any good if you have the short version. my 5ft one would stick miles above the roof line! However I cannot fault it, it is greaseable, I had it galvanised (wasn't to start with but a much older version), and I am hoping will last me many more years to come.
 

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