I have acquired a new fork for my Schwinn Super le Tour 650b conversion. The original fork 26.4mm race. The brand I used was a Tange Seiki. I see that replacement races are available in 26.4 and 27.0, which I now need. So is it as simply as replacing the race with the correct/new size and using the rest of the headset? The headset was put in new this Spring. The reason for the new fork is to use a taller Nitto stem.
Thanks!

Is there a reason why you can't move the original crown race to the new fork? If it's damaged (fretting damage is common on crown races; the first place a headset will show wear) you can replace it. The only other concern would be stack height. Make sure your new fork has a long enough steer tube to accommodate your headset. If it's only slightly shorter than the original steer tube, you may be able to replace the whole headset with one having a shorter stack height, but you can only fudge a few millimeters in this manner. If the new steer tube is longer, it's not such an issue, as you can fill the extra space with spacers or trim the steer tube to fit (measure twice, cut once!).

Tap the appropriate size crown race down onto your new fork and put it together.