I really hate to tell you this, but that engine is going to come loose when you start it. You can make the top removable by gluing basswood on the inside and screwing it down. The issue here is that the firewall on my Avistar trainer was thicker than the one in the Yak. I had this plane with the DA-50 and 5945's and it flew awesome. But the firewalla came loose twice, even though I had DOUBLED the firewall with 1/4" ply and tristock on the back and front, twice as strong as yours and it still came loose. I hate to be a pooper but you need to work on that firewall. You need to thicken it from the inside so that it doesn't throw off your standoffs and makes the engine stick out too much. The stock hardware on this plane is fine except for the pull-pull ball links, this rudder is too big for that kind of cheap plastic. My rudder just peeled off the threads on the inside of the ball link. Attached are pictures of mine! I loved it its the best 3D plane I ever flew! You;re gonna love it and if you want it to last PLEASE reinforce the firewall. Good luck!

Vic