G`day ffj
I`m in aus so things are different here, i know a clear title for each bike is important over there so if your going to rebuild one or both i would check that. Your other choice is to buy the bikes and part them out, i used to be against this action but have realised that that is the only way my bike has got to the point it is and many other bikes wouldnt be on the road without folks doing that.
When you have two bikes to work with you can pick the best bits of both and put them together for one decent bike and the leftovers are "playtime" parts for another project.
The auto`s are something i have no experience with, but i can see them being an easy ride in any sort of city traffic.
Go for it mate, that could be a real fun project...