The "triangle pieces" are the tail sections. There should also be some ruddervators (conbination of rudder and elevators) to match up with them.
Looks like the previous owner put an extra fuel 5gal tank on it. It's possible that it could be two 2.5gal tanks, but they look bigger than than that to me. why does that matter? Remember that FAR Part 103 limits ULs to just 5gal of gas.
Overall your Lazair looks to be in good condition, but be very certain to look things over to be sure. Read the threads on this site and you'll find a lot of good information. The guys on this site can litteraly help you with anything that you will need to understand, restore, and fly your Lazair.
Good Luck,
Dave
B034