Thanks for the info and opinions everybody, lots of food for thought. One thing I am always careful about is good restraint attach points in the aircraft structure, although fortunately I've never had to test one. Also, this 1913 monoplane has a cable braced upside-down V cabane in front of the cockpit for wing brace wire attach, and that should be good rollover protection. Re the practicality of pre-WW1 airplanes, we put about 150 hours on the replica 1911 Curtiss Pusher in 2011, and about 5,000 miles cross country. It is a major effort though, with a lot of planning and support, and requires a little cheating, especially by using a modern engine (we liked to joke that 1947 was "modern"), http://elycurtisspusher.com/
Fortunately the Curtiss had good places to attach belts and harness.
I'll post pictures of the project when it gets far enough along.
-