The only way to make it fit with the pull start is to shim the engine up. The downside of that is you cant use a starter box if you want to. If you put the back plate on you can use the HPI pull start which is smaller and it will still work with the starter box as well. That way you have the option.
If you are having trouble getting it to turn over with the pull start you can loosen the glow plug a little to reduce the pressure. As soon as it starts tighten it back up.