Audio Research 230/240 volts

You should be fine with that piece. Even if the transformers weren't the same, the lower voltage unit would only operate at a slightly elevated temperature as there is only about 4% difference in the ratings. Many of the older Audio pieces over here were designed with 110-115V X-formers/power supplies. Now normal residential voltages are running 120-125V(an 11% disparity), and the function of the equipment is not affected.

As I write this, my PS Premier is telling me incoming voltage is in the range of 239-241V whereas it is supposed to be 230V here in Germany. It has been showing that every day for 11 months it has been in my system. So it would seem, before I had the Premier, I've been exposing gear to higher voltage for years without knowing it. This has neither affected functionality nor the life cycle of any component. Sonically, with the Premier in the system the performance is cleaner, but I'm convinced that would have been the case at 230V incoming voltage as well. However, especially tube gear did run noticeably hotter previously when plugged directly into the wall socket.
All in all I think you can safely go ahead.

You will be just fine.

I've recently imported two pieces of ARC equipment from the US (an amp and a preamp) and have had them converted from 120 volts to 230 volts (according to the specs on the transformer)and am running them at 240 volts without any issues. BTW, both of the units use universal transformers so that voltage conversion was simply a very straightforward matter of reconfiguring the wiring on the transformer in each case. I had it done by an audio technician for vey little cost. I suspect all ARC equipment uses universal transformers, so don't believe it if you are told that voltage conversion of ARC equipmnet is going to be an expensive exercise.