The Poulan 33cc is a cousin to the 42cc, and I have converted that one. If I remember right though, the magneto mounts to the saw body, so you will need to convert it to electronic ignition. That's best anyway. Yes, you can easily convert it to a Walbro carb. A carb with an 11mm venturi would work, but a 12.7mm venturi would be best, and make sure it has both high and low adjustment needles, as some of the newer carbs don't.

Where it came apart at the crankcase, carefully clean any old sealer off, then apply a new sealer such as Yamabond or Loctite case sealant. Put it back together and you're good to go. (You'll need to shorten the bolts that hold the crankcase halves together.) Try to make the crankshaft end seals seat in the same spot as they were.

It will make you a good engine for your airboat.

AV8TOR