I'm sure this is a stupid question, but are JIS and ISO fork crown races interchangeable? I mean is everything else the same size and it's only the crown race that's got a different inner diameter (so if I have a JIS fork and and ISO headseat, I'd only need a new fork crown race) or is everything in a JIS headseat also larger to accommodate the extra 0.6 mm inner diameter of the fork crown race?

My guess is I'd need a whole new headset (or at least the bottom half), but thought I'd check to make sure. Because I have a tall 26" wheeled mtb, I'm having a hard time finding a replacement fork. Finally found one online, but am having a hard time figuring out this one dimension from online sources, so I was trying to see if it'd matter or if I should just order it because replacing the crown race would be easy.

I'd imagine that most threaded forks produced nowadays would be ISO, but you never know and I've learned not to assume if it's not spelled out.