I have a 1991 Diamondback Apex that has a very aggressive geometry. I would like to raise the handlebars and reduce the reach. Does anybody have any experience with this? I have already raised the handlebars as much as the stock configuration will allow. The stem and tube are one piece. I am thinking I will need to replace that integrated piece with something taller and possibly adjustable. Want to make it more comfortable to ride.

You could do something like this,

Yes, something like that is what I have in mind. Looking for technical details of how I would do that.

I didn't change the stem, since it holds the front brake cable outer. I don't know what exact bars I used, it was old when I got it.
Check out Soma Sparrow bars, they are pretty close. You'll probably have to change some cables.

I was thinking I would need something like the following:

https://www.benscycle.com/zoom-quick...iABEgLHIPD_BwE

And I think you are right that I will need new cables.

This is what I did for my buddy's DB, a taller quill riser stem with a riser bar. The difference in reach and lift is considerable, and the greater sweep of the bars also helps. Both stems are at the max height marks.

I just used a quill stem with less reach and more rise. It did not have the cable stop built in so I used one that went below the headset nut. I think this is a 1992 DB Apex.

Is there bicycle specific cable stop that would work for this application? Or do you have to find a generic cable stop that has the right dimensions and make it work?

Something like this. As long as your headset is 1 1/8" and you have room in your headset stack. You may need to loose a washer or reflector.

Mine is 1", but this put me on the trail and I found what I need. Thanks!!