I just read that the 900 is on 91 octane which surprises me.The fuel system for pump gas is much easier than it is for E85 with about 30% less flow requirements. They could either voltage boost the stock/OEM or add an extra pump. Or they may even have enough extra capacity to stretch the OEM system out to make it work. I'm sure they probably upgraded the injectors (to go along with the whipple 3.8) but it's not like the GT500 fuel system would have to be totally overhauled to get adequate flow for 900 on pump.
I'm more curious as to how they got to 900 on pump in terms of safe/reliable (and 50 state legal) tuning.