I would suggest not just looking for the largest 2-blade, but finding one harder than normal. Most broadheads are left quite soft for ease of sharpening with a file and impact survival.
If a file cuts it, it will not hold an edge very long as a knife. This, of course assumes you are just going to put a handle on an already heat treated BH. If you are going to re-harden and temper, then it becomes a different story entirely.
As a broadhead, it needs to cut once. As a knife, you would like it to cut multiple times before it has to go back to the stone.
Just the thoughts of a hobby knifemaker.