Haven't used a machete to make a bowie yet, but I did make a nice kitchen knife from an Ontario 10" field knife. Thinned the blade a little to make it a better slicer and put a birdseye maple handle on it. My kids call it the machete knife.
I am planning to do something similar to an Ontario 14" butcher's knife (Old Hickory).
Like jackknife stated, work slow and keep it cool.
I had to drill new holes in the tang for hidden pins. The tang was also hardened. I spot annealed it to soften so I could drill the holes. I put the blame in a bucket of water, deep enough to cover any part of the blade that I didn't want annealed. Hit the areas where I wanted to drill with a propane torch, let it air cool. Drilled easily.
Have fun making your bowie.
Ric