I mounted mine in a similar fashion, with a duplicate steel plate on the underside. Instead of welding the allen head bolts to the bottom plate though, I just cut threads into the 1/4" steel plate and threaded the bolts in from the top.
It does make for a nicer looking install. GC goes to a lot of trouble to make such nice parts it seems a shame to cover them up.
I notice your parts came with a nice GC logo and, what looks like, double hole oval shaped washers for the adjustable section. I'm I right on the washers?