Most gas combination valves for hearth appliances are rated for 175F. When you change the bracket, you don't know the heat signature on the new valve do you?
I've battled with some of this BS before and decided it wasn't up to me to design and build a new appliance. If the mfr. cannot provide the proper parts, I recommend full replacement. You take on a huge liability when you fabricate brackets and make modifications, even if so instructed by a mfr.