Get your questions answered.
Ask the boss how much of the job is doing what you dread. Explain to him that you dread it -- but can do it -- but it would not be your preference.

He may say that it is a small part of the job. He may say that those duties could go elsewhere if you're thinking about turning down the job because of that 1 duty.

Then, what you call a curveball -- I call an opportunity!