The following post on the MTFCA site gave me a start on this effort http://www.mtfca.com/discus/messages/29/47541.html
Using a steel firewall, how would I build a cowl that would attach to the firewall, and also the wood body. What I decided to do was utilize the wood firewall I already had as a wood spar, and then make a duplicate, but slightly bigger spar to support the dash. If you look at the vintage speedster photo, we are not looking at a significant amount of weight or metal to support.
Using a compass, I set the width to be slightly wider than the points on the firewall where the brackets mount. I then traced this same pattern onto the wood firewall. Using a bandsaw, I then cut out this pattern.
Ack! The steering column! So I stopped, mounted the steering column onto the wood firewall so that I could then get the diameter of that mount, and cut it out,
Off to the bandsaw I went.
Here is the result, with and without the coil box mounted to test fit (Yes, I know that is not a 1922 coil box.)