I'd sooner stick a big dirty super charger on her instead!
Seriously though, My Da had a big volvo that ran gas or petrol for a couple of years, there was no difference in performance when he had gas which wasn't often, but she was a big guttless heep either way, he crashed her after have two years of trouble free driving, but as I say, mostly on petrol!
There are grants that you can get, but they only cover part of the cost!
Do you really drive her that much that it would be worth the hassle??
Dan