Don't strip the white paint off a Faber. It's not worth the hassle. Accept the aging of your tanks - most of you posting are not going to run out at the first sign of a wrinkle and get your face Mickey Rourked now, are you?
When you get a new hydro stamp, just spray a little white Rustoleum on the bare steel. If you want to make it more legible, go over it with a black grease pencil and then clean up the area so just the grooves have black gunk in them.
If you waited too long and have a little rust on the outside, just wire brush it a little, clean it up, and zap it with the Rustoleum.
The ZRC is an estimable product, but unless you are the epitome of Total Anal Diver (pronounced tard) and require spotless dive gear, you do not want to mess with this. The stripping, the surface prep, applications, and the subsequent air cure with drive you up the wall. Sell your painted steels - you'll get a good price for them and pop for galvanized.
There is a lot to be said for galvanized steel tanks. I got my painted Fabers pretty cheaply, I had a small wire brush, and a can of white spray paint was pretty reasonable.
For the guy in central Florida, there is a guy who is genuinely going to hydro fire-blackened scuba tanks??????????????? Well, it is pronounced Flor-i-duh.
Good luck with all that.