Very impressive numbers! Yeah, I would epoxy some triangle stock behind the firewall.
And, go over all glue joints; make sure you have the wing center section wrapped with glass cloth, etc.
I put a pipe on my Super Tigre .40 Bluehead. It's already turning a 10x6 at 14,111 with a stock muffler:
With the pipe I expect to break 15,000.
It might be interesting to lengthen the header and see what it does with an 11x6, too.
I had to send my Canon camera in for service, so this is a poor quality cell phone photo.