This is not a simple hacksaw, drill-press build is it? Pat.
If you're using a hacksaw and a drill press to assemble an AR, you're not doing something right.
If a stripped lower is transferred simply as a receiver, I was under the impression it could be built in either configuration.UH, yup
But to the original post, to build an AR pistol you need to buy a "pistol" lower. It is identical in every way to a "rifle" lower except that when you had it transferred to you from your FFL dealer it was transferred as a handgun. I'm not sure if you can convert a lower to a pistol lower. You probably can (???) but I simply don't know how.
There are some parts that you need to be careful of when you build an AR15 pistol. NO buttstock can be put on the gun. NO vertical forgrip can be put on the gun. If I was to build one now I would want an Olympic Arms or similar upper which eliminate the buffer tube/assembly/spring on the rear of the gun and move the recoil system up over the barrel. It makes for a more compact handgun, and one that I think is easier to use because the buffer system doesn't stick out behind the gun.