I've never used to wire bindings with the tapered 'cut nails' as wedges to hold things together while soldering.
I use 2 pieces of 3/32 square steel stock. One long enough to run the full length of the top rib and another shorter one for the bottom rib , muzzle to the front of the FE lug.
The square stock lays nice and flat and doesn't roll off the rib surfaces.
I C-clamp the pieces down onto the ribs. Just snug enough to keep the ribs in place.
I clamp the bbls together from the side in 2 different places, one being right near the muzzle. Simple screw tightening hose clamps work fine for this.
The bbls and ribs are tinned,,I use an electric soldering 'gun' to do the chore. It goes very fast and efficiently. The only place I need to use a propane torch to tin is the bbls right by the FE lug and behind where the short bottom rib section goes. Just a bit to heavy for the WEN gun to tin them.
I flux every thing before setting the ribs and clamping them in place. An extra clamp is over the FE lug. A short section of the sq stock holds the bottom short rib in place with a clamp as well..
I stick a tapered wooden plug into one chamber of the bbls. That is secured in the vise holding the bbls horizontal. With that I can turn the bbls as you solder, upside down/right side up as they swivel on that plug.
One end is always cool enough to grab onto with a gloved hand as I solder the ribs down with a plain old propane torch.
I start from the breech and work to the muzzle. The ribs will elongate because of the heating. If you start at the muzzle and work back to the breech you may find the rib is slightly too long if it is to fit up to the brazed breech section of rib.
Get the breech sections to temp and then watch for the flow of the solder.
Slightly tighten the clamps as you get to them to secure the rib down. Add a touch of solder if needed, I hammer the end of the wire solder out to paper thin. That melts and flows into the joint very easily.
Keep working forward to the muzzle soldering and tightening the clamps if needed.
Don't get anything too hot or the flux will burn and the job is spoiled.
I use plain paste flux as found in DIY stores. Same stuff I use if (God Forbid) I have to do any plumbing work around the Casa. Hate doing plumbing work..
Solder is either 50/50 or 60/40 Lead/Tin. Nothing special.
I've used the 95/5, Tin/Silver soft solder and didn't find it much different using it than the Lead/Tin.
They say it's stronger, but is that really a need. One thing I don't care for about it is that any solder seam line will stay Bright White.
Doesn't look all that great in my opinion. The Lead/Tin will oxidize to a dark grey/black and look better on the finished product.
Solder all the way to the muzzle, checking the bottom rib as you go by swiveling the bbls on the plug.
I leave the muzzle open when I'm done relaying the ribs. No solder filler, no steel keels if they were in there.
I leave them out untill the bbl's are blued. Then go back and seal it up. The electric soldering gun is plenty of heat to do the job and I don't even bother to clamp the muzzle when doing this
The reason I leave the muzzle open is for water drainage when rust bluing. Many bbl sets already have a weep hole or 2 in the bottom rib, but the open muzzle fills the rib cavity and then drains it very efficiently.
A final rinse when I'm done is to use Washing Soda in the tank water and let the bbls slosh around it that for a while. Then a clean water rinse and dry.
Washing Soda is Bicarb of Soda's big brother. Sodium Carbonate is what it is I believe. Another product avail in grocery and DIY stores.
Much more alkali and a better neutralizer.
It can sting your hands especially if you have any open cuts. Don't get it in your eyes!
I still heat the set with the old propane torch again after They are done.
Any water trapped especially up by the breech section will simmer and steam out.
That same wooden plug is used. For this I tilt the bbls upward with a slight forward cant. That way any water that spurts out of a weep hole on the bottom when it gets hot can be caught with a paper towel and won't discolor your new bluing job.
Well that's how I've always done it. It's just another way to a result.
Like most processes in this trade, there are more than one way to do them.
It's the results that count.