This is the internet and everybody is an expert. You are free to follow or ignore all advice which is offered.Tell you what,if you want to do a good job of parkerizing there are no shortcuts.
First, thoroughly degrease the parts in laquer thinner.After having done that, only handle the parts with rubber gloves to avoid contamination from fingerprints. Next,sand/beadblast the parts to remove old finish (wear heavy rubber gloves for this) and to activate the steel surfaces so that the parkerizing will react well with the steel.Also,I pre-heat the parts in the oven @ 180-200 before immersion in the park solution which seems to assist the process.
A good parkerizing vessel for all parts,but a barrel or op rod, is a large oblong shaped electric crock pot with ceramic liner.This is non-reactive with the park solution and allows you to regulate/control the heat of the solution which is critical to success.Use a candy thermometer to check temp and degreased stainless steel tongs to deposit/remove parts in solution.
Lastly I would not play with "home brews" or do the job indoors on a kitchen stove.Parkerizing solution is acid based and one should do this outdoors where fumes are not an issue.Get a proper parkerizing kit,rather than try to roll your own.A manganese based solution will produce a blackish color,while a zinc based solution will result in a grey color. This is not hard.It does,however require the proper equipment and attention to detail.