I guess, If I had a "normal" anvil, I would not have to answer the question about what I want to do with the horn.
It is not easy to answer. For what I made yesterday, a 1 1/4" black iron pipe was almost the right size. I had my "anvil" on a stack of bricks, and I tried to hold the pipe on the base of the anvil with my foot, while I used it to form the loop on the rake. It sort of worked. Then I wanted to make the loop smaller. I used needle nose pliers and made it look worse.
For the loops on the adjustable "stock support" on the side of my forge (idea from the book A Blacksmithing Primer), I used a T-fitting for 2" iron pipe. It was larger than I wanted but all I had at the time that wouldn't start on fire. I had to put that in my bench vise because I had no other way of holding it in place.
In the class I took at the Campbell Folk School, I made a bell from an O2 tank. The bell clanger and supports had several loops of different sizes and U shapes.
So you see, I don't have any one particular thing in mind.
Yes, the pipe support forming the center of my "anvil" can be used for large loops, as can the round edge of the top. But they are only one large size, and moving the anvil (flipping it) is not something I can do once it's fastened down to the stand I will be building. I have considered grinding down the top and bottom edges of the top plate at the rear (opposite the hardy), and attempting to taper them such that I had a range of sizes to use, but the utility would be limited by the plate itself (and reduce mass in the area which gets the hardest blows.) I rejected that idea.
The only things I've come up with (besides purchasing a cone for the hardy hole--which isn't steady, as I said), is some contraption similar to what you mentioned to me on the welding forum, but with a number of sizes of rounds, all lined up together and welded onto a piece of angle, then with a hardy post on the bottom. So I would have a range of sizes, but again, limited to only one section of a loop (and also not well secured in the hardy hole). And yesterday I found that cast viking anvil from vause, which almost looks like it could be made to work in the hardy hole. I guess I'll send them a note and get more details. Sure seems like I should be able to find something at the recycle yard that would work, since my goal has been to make most of this from scrap. Imagination may be lacking.
-Q