First of all everything Brownells offer is good stuff. Some is better then others, but they don't peddle junk, and what they do sell is checked out by they're in-house technical staff.
If there is a machine shop or someone else that does sandblasting in your area I suggest that you consider one of Brownells' Parkerizing kits. You can safely Parkerize on any stove or heater where you can boil water, and the process is simple and straightforward. The usual color is slate-gray, but they have an additive that will make it black. They will also send you a free copy of the instructions if you request them, or they come with the kit of course.
Sandblasting is not necessary, but if you don't do this you will need to remove the old finish with a chemical dip - also available from Brownells.
An additional alternative is to Parkerize the parts as a prime coat and then finish them with one of their spray-on paint type finishes. More rust protection, and a "slicker" surface inside the magazine body.
