The bike doesn't appear to have horizontal drops. That means you would need a chain tensoiner, which takes much of the "simplicity" out of SSFG.

The best candidate for a conversion is a bike that's in good condition with mostly servicable parts but has lived out it's usefulness as a geared bike. In other words, your old mtb has been replaced by the latest disc brake DH monstrosity. Try finding an old Specialized Hardrock. They can be had pretty cheap, the drops are horizontal or can be made so, and they aren't too crappy.