yeah, that doesn't help either.
need to know width.
i have a feeling you're going to say somewhere in the 7 to 8 range. so, assuming that, no, +40 is not a good offset. It will look sunken in, and depending on the wheel, you may have suspension / brake clearance problems.
Aim for something in the 25-30 range for easy fitment on a 7/8" wheel. If you can't find anything like that... buy the wheel, put it on, measure how much farther you want it to be out or how much room you need to clear suspension or brakes and then head to
http://www.wheelspacer.com and get some made. He makes some of the most awesome spacers you'll ever see and they won't create lots of problems inherent in like sandwich spacers or something like those.