Those are two good links and well worth reading for anyone re-building any of the big ordnance. For one or two pieces, the first method is the cheapest and easiest. Just about anyone can do it. The biggest drawback is that it is sometimes difficult to find the correct lettering size and style unless you have access to a big art supply store. If you have several pieces to re-build you are better off to buy a stamp kit and roll stamp like the originals.
The biggest mistake most people will make is applying too little markings. Especially for USN projectiles. The markings on those must have been designed by 5 committees. They are marked both front and back. Even the one I show here (front and back) is not complete in that it doesn’t have an ALN (Ammunition Lot Number), but I was not able to find a photo or drawing of an original to use as a guide. Another common mistake is using the wrong colors which changed constantly. Photos of originals are a big help here.
There is a world of difference between big ordnance that is re-built and those that are all dungy, rusty, and missing a piece or two. Some may call it sacreligious to do this but they deserve better treatment, IMHO.