The answer depends on the length of thread, and how far you plan to insert the stem.

Most headsets require close to 3/4" of thread, so you're at the borderline, and first need to test that the top bearing threads down far enough. If it does, then you can use extra spacers above, or trim off the excess at your option (don't trim too close, since you can't re-trim it longer, cut long and use spacers to be safe).

The second part is critical, the stem must extend 1/2" beyond the lowest thread if it's the split with cone type, or much more than that if it has a tapered wedge. That's because the threaded section of the steerer has less than half the strength of the unthreaded section. The stem must reach well into the full wall section to transfer the load without breaking the steerer.