I measured about 30 uOhms (with a 34420A, and the original 10 Ohms SR1010 and shorting bars; hard to measure precisely of course). The manual states 50 uOhms appr. value. As per their spec, and I have never checked / questioned their calculation, as I would think errors would have been identified by now, this still leads to the 1ppm spec you referred to.
In any case, the 10 Ohms SR1010 is a very good way to transfer 100 ohms to a precision 1 ohms resistance standard such as a Leeds&Northrup 4210. So no good idea to destroy it. Good you are beyond that.
Building a shorting bar yourself is ok, but no way arround heavy gold plating.