Originally Posted by Retro Grouch
I assume that what you are talking about is what's called a "conversion quill". I've got good news and bad news.
The good news is that the lower portions come in sizes to fit 1" or 1 1/8" forks so be sure to order the right size (I assume 22.2mm). The upper portion also comes in sizes 1" or 1 1/8". I'd get the 1 1/8" because that's what most of the threadless stems are.
The bad news is that from looking at the pictures it doesn't appear to me that you're going to get very much vertical adjustability from using one.
+1
There is virtually no vertical adjustment on those things. If you are moving the stem up and down, then you aren't fitted correctly. Once your bike is set up properly, you shouldn't have to change unless you add a new part. Nitto makes some beautiful and really tall quill stems. They work perfect on a touring bike.
The only other way to use an ahead stem is to buy a new uncut fork and headset. You could have a competent frame builder take the stem out of your existing fork and braze another one in. Now you are starting to get into some money. Stick with the quill set up. Good luck
Tim