I had already bought a piece of strap metal like you show, thinking along the same line as you.
Wish i had started playing around with this earlier in the fall, it is a little hard now that it is cold. I would have changed my design on how i have it set up. It does heat well, and i think it is very efficent with all the cast iron mass. Now i must confess to something, when i bought this house in 79, the old coal bin was still in the basement along with some coal. If i remember right, i believe the old grates and lower door were in there and i threw them out. If only i would have kept them.