If you search RCU for "UltraStick 40 engine mount" you will find a lot of information. In particular you will learn that many had mounts that broke after a few flights. Everyone I know, me included, has replaced the metal mount with a nylon mount.

Another mod this model needs is more wood behind the holes in the former that the wing dowels go through. Mine were wallowing out pretty quickly.

The US 40 fuel tank has also split on quite a few of us and you may want to replace it. I have a Sullivan 10 oz tank that is a perfect fit.

The last item on mine is that the firewall pulled out in flight last week. Nothing too serious, but the 1/4" sqaure stock in the corners was little help. The glue on mine was most likely weakened by fuel (see split tank above ), but you may want to think about pinning your firewall through the lite ply on that runs down the middle of the fuse where it goes into notches on the firewall.