NW Ohio is not what I would think of as a tourist attraction by any means.
But since you listed 100 mile radius and mechaincal based attractions, then I too would say to stop by The Henry Ford [museum]. Greenfield Village is historic, yes, but not quite as attractive to a gearhead.
Sauder Village is in my neck of the woods, but quite honestly - it is just a reduced scaled version of Greenfield Village/The Henry Ford [museum] for the most part.
If you've never been to the big tractor pull, that may be a real good time for a crew of gearheads! (especially if you left the wives to home, and have seating in a certain area, and the weather is hot.) And that is right in Bowling Green! (Wood County fairgrounds) I haven't been there in many, many yrs now. My dad pulled there once with a turbo'd 4020 back in the 70's. But the super mods are always impressive. (I have no clue how someone can justify playing in that circuit tho)
Otherwise - LOTS of corn to be seen in every direction from BG. Not exactly Illinois, but you are in the heart of our corn fields.
I haven't been through the canal tour thing in Grand Rapids, Ohio (drove past it many times tho) but that may be of interest to your crew. (as posted above)
The only "claim to fame" that we have AFAIK to "tourist attraction" in NW Ohio is Ceder Point, but somehow I don't think that's quite what your looking for. (Not been there in 30 yrs?)
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