One of the drawbacks of the American-made three speed bikes is the bikes often come with stems too short to allow for much handlebar height adjustment. The British three speeds often come with stems allowing a bit more bar height adjustment.
On taller frames, this may not be an issue. For example, this 1960 Schwinn Traveler has a tall frame and, unless the rider is very tall, the bar height generally does not need much adjustment.
In contrast, this 1950 Schwinn Superior has a "standard" frame of around 22 inches. The chances of a rider wanting taller bars, whether due to rider height or wanting a more upright ride, is greater with this standard-sized frame.
In those cases, I recommend looking for a taller stem. In some cases, originals are available, but sometimes a good reproduction or a newer stem will also work. In this case, I am using a good quality reproduction of the Schwinn "razor" stem that is substantially taller than most of the originals. This gives me a substantial amount of handlebar height adjustment, so I can set the bars how I like them. These stems are still sometimes found in unused condition on eBay the Classic & Antique Bicycle Exchange, and other sources. Many were made for reproduction Schwinn Phantoms and balloon tire bikes in the 1990s. The quality is not quite as good as the originals, but it is still much better than most reproductions. I tend to prefer a more upright ride in the style and tradition of the British utility bikes and roadsters.
Other options include stems from Nitto (good quality), Sunlite (passable quality), and generic makers (usually pretty rough), usually from Japan, Taiwan, or mainland China. I recommend spending the extra money on a good stem. A stem failure or improper fit can lead to accidents and serious injuries. If you are unsure on how to source and fit a stem properly, get help from a competent mechanic. You can severely injure yourself if you improperly fit a stem.
A good quality seat post also should be used if you plan to raise the saddle more than a few inches. Schwinn originals are generally good, but even better are the modern BMX-inspired Cr-Mo seat posts. This particular bike has a Cr-Mo seat post from Porkchop BMX shop. It has the usual 13/16" Schwinn frame size, and a 7/8" top for use with standard saddle clamps.
Even with this additional adjustment, some riders are just too tall for the standard 21 or 22 inch frames. In those cases, the rider should go to the tall frame bikes, even if those are more difficult to find today.
The bottom line is that even though you may own a vintage American three speed bike, don't be afraid to make the ergonomics work for you.