Decon will not hold your Grilles. The straight on section you repaired, needed a back brace. It will break upon installation or later when the road vibrations occur. Sorry to be a bringer of bad tidings, but the 69 Cuda Grilles are notorious for recracking once installed into the cars, if you make it that far.
The best epoxy on the markets are the ones that advertise their PSI rating, such as JB Weld. JB Weld has recently put out a Clear 2 part epoxy that has the highest PSI strength rating in the industry.
Congrats on redoing your orig 69 Cuda Grilles, it was a wise choice. The reproductions are a total nightmare. It is amazing that the guy chooses to keep them on the market. Really bad stuf, nothing even close to the originals.