Brad, I started with one not much better. I had to replace 90% of the wood, and yes. I will be "Upside down" in it when it's done. You can see most of the work I did in my album "My A" I tried to put the pictures in such way that it would be helpful to someone else doing one of these.
The Wood! The wood is probably the most daunting of the steps, stages, and or assemblies that are involved, But it's not insurmountable! I did buy my top wood and the sills. Pretty much the rest of it, I made. If you should try this (And I would suggest that you do, if possible) You must duplicate the sizes and curves exactly! And there is hardly a square angle on any of it.
The seats! The seats are basically a simple wooden frame with a spring on it. The seat spring (F) is relatively easy to make from a mattress spring with some modification and welding. That brings me to another necessity, You're going to need a small MIG (wire feed) or TIG welding machine. The thing you'll need the most is the ability to hang in there. Some of it will go quickly and you'll be happy, some of it won't. You will have learned a lot by the time you're done!
Terry