Just realized my answer is a little lengthy but here goes!
Easy to place hinge behind pipe with existing design. Just rotate pipe before locking with support post bolts. The cross bar is not welded in place for ease of disassembly for transport. This will also stop some of the swing (which also might be important if you can possibly get them all swinging at the same time at long distance, I am not that fast at it at that range). But then again all shooting is done with my Savage .308 FTR at 600. It is not a public use target at this point. The Savage is working well took 5 shots but managed to hit a golf ball at 350 yards last week in cross wind, I saved that ball. Ipod ballistic program was just about right on.
My existing gong is a 3/4" - 12" mild steel with the same length of arm and no hits have been close to the hinge, so far. It works well as the sighter to figure out wind before moving to small targets when painted, hits are easily seen with spotting scope as about 1" black marks on the steel at 600. I was given the piece so don't mind using mild steel, surface does get pitted.
Lucked out on AR steel, cost for all 6 was less than $100.00.
I have 3/8" AR 400 - 4" circles, some slight surface dings from my AR 15 and .308 after a few hundred rounds, still lots of life. The slight angle on the support arms of the pictured target goes a long way to reduce impact and extend target life. You need quite a bit of heat with the torch to bend the arms though. If I was shooting at 100 yards with .308 I would probably get AR 500, which I know will not surface damage at all. Availability and cost are the issue with the 500 though. I can replace and turn targets to use the back side for quite a while and still be less than the cost of AR500 from my supplier. There are no off cut pieces of 500 I would have to pay full price.
See my other post on good day at range Manitoba style to see those targets to get an idea of damage.