Thanks very much to all of the above for the advice & insight.

To provide a bit of background, I'm mechanically proficient with cars & motorcycles, and I'm pretty competent wrenching on bikes in terms of doing necessary work without breaking stuff - but I don't have the encyclopedic knowledge of different sizes, shapes, etc. of the various components and what will work with what else. I'm a pretty avid cyclist and last year bought my first "nice" bike - a Jamis Sputnik after years of riding beaters. I'm planning to do a 100k Gran Fondo with my bro-in-law this summer, and I think it would be more fun if we did it on some passable road bikes instead of me on my fixed gear bike and him on his heavy-ass wrong-size 90's MTB with cheap slicks. Last year we did back-to-back century rides on successive days on those two bikes and it was fine, but with the Gran Fondo comes the chance to set an official 100k time and it would be fun to do it with halfway-appropriate bikes.

There's a Nishiki Continental for $80 on CL that looks like it would respond well to a few weekends of cleaning, lubing & polishing. Does that count as an in-bounds Japanese bike?

There's also a nicer-looking Cannondale ST400 that looks like it's ready to roll right now for $230. But nobody mentioned Cannondale above as a good choice.