The Four Star 40 comes with a 2 piece glass-filled nylon mount. One of the better made ones you can get... If the engine refuses to sit level on THAT mount... you did not put the mount on straight (one beem one height the other a different height... if its crooked... its in how YOU put it on.)
The engine mount off of the Avistar is useable on the Four-Star if you can't figure out how to get the Sig mount on straight.

The 4*40 has a nearly straight thrust line... just a bit of right and a bit of down built into the firewall.

"extra parts that should have come with..." What parts? was it the "kit" or the ARF? The kit doesn't include a fuel tank or wheels or a few other things that would be in the ARF package. The ARF still needs a few items, but not much other than your radio and engine.