Nice!

I suspect the success of an upside-down fire has something to do with the type of wood, and more importantly, the dryness of the wood. With softwoods that are not kiln dry, for example, I think it would flop.

Enjoyed the traditional bucksaw design. Nicely done. Always wanted to make one out of field materials. What did you use for the tensioning material? The antiques used a heavy, stiff wire. I'm not sure what other material would be suitable. If the tension is too low, or the material to springy, it would be easy to put a nasty kink in the blade, and then you're sunk.