That shaft coming out of the back is commonly used with a spring recoil starter such as B&B Specialties sells. It is part of the crankshaft and not removable. If you just don't like the looks of it you can cut it off with a Dremel tool. G-38s start very easy by hand so you really don't need a recoil starter. If you cut the shaft off, re-balancing is not necessary because the shaft plays no part in the balance of the crankshaft.

It's an airplane engine if it has a prop hub on the front. If not, you can order a prop hub from Ralph at RC Ignition or Horizon Hobbies.