You're probably not going to find any EFI info from zilla guys, it just hasn't been experimented with.
TBI is a little different than a carb as far as sizing goes, because you're not worried about creating adequate vacuum at low RPM to meter fuel.
My hypothesis is that a larger bore can be used due to the EFI's electronic nature vs. vacuum operation, and possible power gains to be had because of it.
50mm would seem like a good starting point...