I bought rims of the same weight from Peter, I didn't measure the outside width, the internal width is between 19 and 20mm.
Same hubs, with Sapim CX rays, and I ended at 1218g for my gravel.
Will you use them on your 29er?
I ride another ultralight pair of rims on my 29er for a few months( but with heavier Hope hubs ) and they seems to resist quite well to the hits they receive regularly.