I couldn't give you any better information than Randy has. Poly-Choke
sounds great if they have one with the right contour for your barrel.
If you want to machine your own the proceedure of the Simmons Co. could
be adapted. If the bbl was a straight tube it would be easy to mil a
radius in a solid rib to match the bbl, it's the contour that makes it
harder. Posts can be made out of pieces of rectangular bar stock with
multiple different radius cuts on the bottom to fit the bbl. Cut all
the posts a little long, attach solidly to the bbl. Put the bbl
between centers on your mill and lightly flycut the posts to the same
level. You could use round stock for the rib posts and tap the top
ends to attach the rib with counter bored allen head cap screws to cut
down on the total soldering needed.
If you could get some of the flexable epoxy for the barrel/post
connection that would probably withstand the whipping of the barrel
when fired. If the epoxy does not work out I'd try the lower
temperature silver solder first and if it does not do the job I'd use
the strongest you can find and protect the areas of the barrel you are
not heating with some damp wraps for heat sinking. Practice on a peice
of scrap bbl or tubing until you can attach them quickly to reduce heat
damage.
One advantage in lower price guns is that the bbl is often thicker than
more expensive ones which are made as light as possible and of better
steel.
I don't think you will have much success trying to solder on a solid
rib unless you have access to an oven long enough for the whole bbl at
one go. Then you would put it all together with strips of solder
between and clamp it down in the oven. Heat and serve.
I hope I have been of some help. Good luck with it however you decide
to proceed.
73 Gary