I would go with screws if you have a drill press. Get the screws and tap with the rib.
usually under ribs are only soldered on thin barrels that don't have enough thickness to be screwed on. If you do solder it on you tin the rib and barrel then clamp together and heat.
If you go with the screws, there is a lot you should know about, and if you don't, beware. Unless well versed in the technique, correctly drilling and tapping those small shallow holes in the barrel is no walk in the park.
I have found the best way for me is to lay out the holes, securely clamp the rib into desired position onto the barrel. With barrel clamped in vise and using the drill press, I then drill and tap each individual hole in place without removing the rib, (or shifting position of the barrel) or moving on to the next hole.
This is done by drilling through the rib and into the barrel with only the tap drill. I then tap both the rib and into the barrel, the tapped portion of the rib makes it much easier to enter the barrel with tap correctly centered and laterally supported. Counter sinking rib for screw heads can be done at this time. (drilling out the tapped hole for screw clearance is done once rib is removed)
I find that performing as many operations on the rib and barrel as possible with moving from each hole's first and original position makes the chances of mistakes much less.