I've run HF's 6.5 Greyhound this season on my Rocket VII. It's an OK motor, especially for the price.
They sell one called a Predator, now, which is supposedly a bit better.
Re-powered my TroyBilt Horse with a used 4hp honda GC 160 ohc and it is a sweatheart!
5 years, no maintenance, and I can't say enough good about it!
Good luck
rc