You can add a frame to any of the small packs; NDR, WL/WH, alpine machine 40 or 50 liters. Internal frames are standard on packs over 50L if desired.
there are two ways i build in the frame and foam pad sleeve. on the photo with the tan pad pocket, the pocket is zippered, with the stay sleeves sewn on top. if you think you will be pulling your pad out to use on a regular basis, the top loading envelope, gray sleeve pocket, is a little easier to use.
the blue foam pad pocket is the standard with no frame.
Aluminum stays are all 7075 series Heat Treated aluminum. cut to length to fit your back. Several stay dimensions are available.