Frybrid claims they have a system for the 6.4, but what bothers me is it's the same kit they use for 6.0's supposedly. A bunch of guys from the vegistroke site have sent inquiries in, of course they don't respond.
I'd wait for the vegistroke for the 6.4 myself... Why put an inferior system on? Have you priced out how much it is to fix a stock fuel system on a 6.4, I wouldn't want to take a chance destroying anything in there to save a few dollars on fuel with an inferior system.
The 6.4 kit should be out pretty soon. Clay Henry is burning WVO in his 6.4 now with one, but it's being redesigned.