The spout is threaded into a bushing epoxied into the small end of the horn. You can get valve spouts for them and I can furnish one for the next larger charge than you want, so you can cut and file to get a proper load.
The base plug is hardwood, hand cut to the natural contour of the horn, not lathed round and then the horn steamed to fit it. I epoxy the base plug in place and then pin it with brass pins. The base carries a filler plug threaded bushing, which is epoxied into the proper place in the base plug and the filler plug threads into that. There are two sizes of filler plugs and I use the one that fits the esthetics of that particular horn, in my eye.
I buy raw horns and sand and polish them. That takes about 10 hours per horn. I then "dip" them to see where the interior cavity goes and cut them. I let them sit for awhile until the contents of my "pretties box" starts to talk to me. Each horn will take a particular set of pretties to set off its own figure and coloring. I scour estate sales, flea markets and second-hand stores for old jewelry, broaches, pins, etc to put on horns. I keep a look-out for hardwood scraps that would look good on horns as base plugs. (I have 3 pieces of Manzanita left, waiting for horns to "call" to them. I have one piece of birds-eye maple left.) It generally takes me 20 to 30 hours to make a horn. I try to sell them at gun shows and shoots, but my personal collection grows steadily.
I'll hit a show with 6 horns, marked $165 each and sell them over a couple of days, the most-dickered one going for not less than $100. Lessee, at 30 hours and about $30 for material, that means I make, what $2.33 per hour?
I guarantee them for 100 years. The warranty reads, "Bring this horn back in 100 years and I will rebuild it."
I'm sure that is more information than you expected, but you should see my response when you ask about my .45 Calibre Flashlights.