There's a great thread currently on vintage-looking motorcycles on the Brass Goggles Forum. Forum member rohorn linked to this beauty from Timeless Motor Company.
The 440cc four-stroke is based on the 1910 Harley Davidson Single belt-driven bike. Basically a complete reproduction with some flash touches like a handmade leather seat, and cast bronze muffler.
And if you look at the picture on the timeless site, this puppy has a pedals... so I guess it is in actuality a monster of a Steampunk Moped.
A fully built one runs about $11k and there are kits available as well.
A Kneeslider article about Timeless.