Running it on 220-240 will not hurt it, short term. But long term, you will be looking for the heating elements to fail faster. A buck-boost arrangement to pull 240 down to 208 is the simplest solution. Since a buck situation is involved, the KVA rating will only involve the difference of each leg. Thereby saving you a few bux. But, there must be an old timey electrician doing the hook-up. The transformer will have eight leads. Find someone that knows transformers. A "bulb snatcher" won't cut it.
Some folks will comment you need a variac or some such. While a variac will work, and work well, the cost of one big enough to meet your needs will drive you to setting up bank jobs instead of machining.