You will need a slide/ barrel bushing that will fit the barrel you want to install.
It will vary with the maker of the bull barrel.
a 1911 barrel, by itself is not illegal, except maybe in a school.....................
the 1911 45 ejector would not line up for a 38 cal. cartridge.
Barrel diameter
Do a search for Jarvis. They make a bull barrel for the $597, it runs $198 in either blued or stainless.
A PMI razzor barrel (spyder thread) will fit your barrel needs. You know it will fit if it is "spyder" threaded.
A heavier (bull) barrel is stiffer than a light barrel. It does not vibrate during firing as a light barrel will. Combined with a steadier aim due to the increased weight, the combination produces greater accuracy.
You will probably have to contact a barrel maker.
Barrels are to small to fit any one horse into it. So no horses can fit into a barrel.
bbl
Yes, the 98 threaded Flatline Barrel will fit the Alpha black.
No Check out the holster to see if its an open front design. Some will fit. There are minimalist style holsters out there that fit any size 1911 Galco, Bianchi..