My data only go to 2010, but at that point the G200 had only ever been made in Japan. By then pretty much all of the GXV160 engines were coming from China, and quite a few others were either China or Thailand. Hence there should not have been any difficulty about product quality with your Japanese engine.
The first series of Honda side valve mower engines (designated with a G followed by a 2 digit number which was not the engine size) were very similar to Briggs engines, though perhaps a bit better and at a higher price. In the late 1980s they were replaced by the series similar to yours, and by then I think they were distinctly better than Briggs. However in the early 1980s the OHV Hondas were introduced, leaving the side valve engines confined to a market niche. Hence I can understand your grandfather's position. The side valve engine would probably stand up to serious neglect a bit better than the OHV ones, and the OHC ones may be a bit marginal for reliability even if not neglected.
It's probably a personal thing: if I'm going to be using an engine hands-on, hearing it the whole time, I would much rather have one that fires every shot - which means OHV, OHC, DOV, or something along those lines. Most people, on the other hand, wouldn't care in the slightest as long as it didn't stop or emit mysterious clanks, thuds, or clouds of opaque gas.
