every one I asked said they did not do a boss for a 2002 z3 even when it said on the listing it would fit. so I took the angle grinder to the old steering wheel its a good 10mm thick steel at the base. I drilled and bolted it onto a snap off hub that I bought for a mini and I even had the mini steering wheel till my new one arrives .on a plus side doing it this way the horn still works in the centre of the wheel and the wheel will remove if your parked in a dodgy area.
just need to sort out a bit of a plastic cover to fill the gap at the back end not to important. I can not make my mind what to do with the dash if anything old school looks good but so dose this in all black.