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.