Typically you will find that the plywood is made up of a number of layers (plys) of wood, hence the name plywood. The more layers for a given thickness the stronger the end product. The Quality of the wood itself is better. Do you think an Oak tree is the same as a Pine and the same as a Birch tree? That is like saying copper and steel is the same, they are both metals. LHS lite ply and reg ply is made with Birch and is the best for this usage, they also use glues in the mfg that are less susceptable to deterioation from the Nitro and oils. Why do you think the FAA doesn't let builders of homebuilt aircraft buy their materials at Home Depot and Walmart and the like? They don't like seeing dead people, too much paperwork. Go to the Sig web site, they will probably have a discussion on plywood quality. They also provide for full scale.

Second, nobody is being a smart alec with you. Mind you, at times it does take great restraint not to say some things. We've offered our help. If you don't want it, just say so.

As for the ribs. IF you still have the pieces that the ribs were orig cut from, you can use one of them for a pattern. Doing that you could cut a partial rib, hold it up against the existing rib and mark the defective rib to cut away the damaged portion. THEN CA the replacement rib section into place. Just take your time and measure and mark and cut carefully. If you only fix one rib each nite, that is progress.
Understood