I have a couple of bars like that. The fellow who gave them to me said they were from use by railroad track maintenance crews. I've made similar supports out of 2x6s.
I like your plan. I need to do something similar because my auto trans leaks badly, and should be refreshed.
I plan to give the K-member a full gusseting while it's out, reinforcing LCA pivot mounts, steering gear mounts, and motor mounts. Maybe add a skid plate. I'd like to give it a hot tanking and powder coat, but it'll probably just get oven cleaner and spray bombing. I'll have to check with CudaChick first.