Stove mdifacation

I read that earlier post about Outdoor Wood Boilers and was interested in the link about a guy who modified hos boiler
to have secondary burn capabilities.
http://www.woodheat.org/technology/outbobpen2.htm
Has anyone done this to a wood burning stove.
It would be a fun project to convert an old unused stove
as a test. Not for real use.
I have an old coal Efel stove. I might try it on this summer.

What are the Burn tubes made of?
What woulod happen to threaded Black Pipe
under those temps?

If my modification's work I would use it for real, but I know it might fail and at some point you but up against the law of diminishing returns, a new stove might be cheaper.
My Efel coal unit is big and cast iron, lots of room to spare inside. It has a small door right above the coal bed for an ash rake, it works great as a primary air intake.
Right now when I am not burning coal but using it for wood, I loosen the door latch so its closed but not sealed tight, and use the ash rake door as a primary supply. I swear I often get the blue floating flames dancing above the fire. Once the stove gets rolling, I shut down my "primary" and with the door just cracked a pinch, she rolls right along.

It would be great to add some real secondary burn tubes and ditch coal all together.