You are probably less flexible than twenty years ago. I would do a few weeks of riding in the drops and on the hoods and possibly you'll get used to being stretched out. After all, the stem fit you once.

When I put modern brake levers on my PSVN (that have a more extended shape than the originals), I initially felt too stretched out on the hoods and my lower back hurt a little. After a few weeks it was fine and I rode 200 miles in a weekend without issue.

Or, if you do a bunch of flexibility exercises and yoga, you might find the 120 mm stem works again. As a side benefit, you'll have spent some months in the company of young women in yoga wear.

But if those approaches don't work or will take too long, there's nothing wrong with changing stems.