Bradd,
I have a few Vulcans and - to me - they seem to be Manganese Parkerized.
Be careful about this information==> I'd try it on scrap first===>
I usually degrease well, sand any rust and immerse the part in diluted Hydrochloric acid (HCl) first. I get it at Home Depot in the paint department under the name, muriatic acid. With parts needing a complete finish, I use sanding and HCl to remove the old finish.
I dilute it roughly (1 whiskey jigger or one once to a quart of tap water) and place it in a plastic jar or jug. I have used the bottom of a half liter plastic water bottle with holes in the bottom as a basket. I punched two holes near the top and attached string to serve as a handle.
If you use a clear container for the solution, you can see the action of the acid, removing the old finish and etching the metal. Knowing you, you won't leave it in too long. When you are satisfied, lift the basket, remove the part and wash in flowing water. The part is ready for the Parkerizing bath.
Using HCl as a stripper and prep bath seems to have worked. I don't have access to a sand blaster so this is a poor man's prep method. It is not as good but it works in a pinch.
Dennis