Reddit mentions of Origin8 Pro Fit Alloy Ergo Stem, 1" or 1-1/8" x 31.8-25.4/28.6-25.4 x 35d x 70mm, Black

The quill stem inserts, doesn't fit on. The threadless headsets and the quill stem headsets are not interchangeable, so you would have to make some special efforts.
Here's a pic and some additional info:

http://forums.roadbikereview.com/components-wrenching/how-measure-quill-stem-125691.html

You insert the stem into the steerer, and then tighten it down.
Alternatively, you could buy a stem extender, such as this,

http://www.amazon.com/Sunlite-Cromo-Quill-Stem-Extender/dp/B000AO7GXK/ref=sr_1_13?ie=UTF8&qid=1412571159&sr=8-13&keywords=Stem+extender

install it, and then install a threadless stem over it, such as this:

http://www.amazon.com/Origin8-Pro-Pulsion-Riser-Stem/dp/B005DNTNPW/ref=sr_1_1?s=sporting-goods&ie=UTF8&qid=1412571477&sr=1-1&keywords=bicycle+stem

That way, you can have your cake and eat it, too. However, the original design is still quite good, and your vintage bike will look better original, unless you want it different. The quill stem is still used on some road bikes (and a few hybrids and mtb's), and works very well.
Good luck. Ask more if you need to do so.

As everyone says, change the stem.

Try this one.

Origin8's ergo stem has the 35 degree angle rise. So, it is shorter, and also brings up the handlebar slightly higher and therefore closer to you. I use 90mm version of this stem on my commute bike.

I can ride a little more upright, and good for commute.