Thanks Randy, tools make the customizing job easier but, back in the day when this all began some pretty wild customs came out...and many times a wide variety of tools weren't always available to the guy doing the metal work. A lot of the improvisation started by these guys is what got the whole hobby going. Bending sheet metal by hand around a pipe to get the curvature you wanted for that change in the sheet metal on the ride they where building. If you look around, there are all kinds of pipes, straight edges, whatever that you can use to get that custom shape your looking for.
There are tools that I wouldn't want to be without, my blocks and long boards are all made out of aluminum, had them for many years and would be lost without them, my body hammers, dolly's and the list would go on, but when it's custom metal work your doing, it's one off work and whatever you have at your disposal to get the job done is what you often need to get to your end goal.
To the OP, X2 on what Randy said if your your planning on getting your custom made bumper chromed, the better you finish your metal, the less your going to pay your chrome guy for your brushed chrome or whatever plated finish your looking for. If you have welds with a minor pin hole, fill it, if the bumper isn't straight, straighten it, the bumper should look as though there hasn't been any welding done. I'm sure you've heard of show quality chrome and that can get expensive. Often show quality chrome on a bumper means that the entire bumper doesn't have any scratch marks left in it from grinding, front side and even the back side. Re-chromed bumpers for collision replacement are usually finished on a 320 grit or 400 grit wheel before they go through the cleaning, copper and nickle processes to give you your finished product. This is fine for daily drivers and will usually look like an OEM finish. Show quality chrome is finished much finer, depending on the chrome company you use, the metal would be finished in 600 grit, or even finer, front and rear. When done, there will not any visible sand scratches in the finished surface. Very similar to finishing primer on a car before painting, if a car is prepped in 320 grit compared to 600 grit before painting, there is a lot less chance of any sand scratches showing up in the primer finished in 600 grit versus 320 grit. The one major difference in chrome plating is that copper is used as primer for the metal versus a 2K primer for painting.
I hope this helps.