Yup, a 50 will fit where a 40 will. A 50 is just a poked and stroked 40. Same outside dimensions. I do not like the TH hobbies engines for a beginner. They do have lots of power. But they can be cantankerous. They have quality control and air leak issues. I feel that they are just to finikey for a beginner. The other reason I don't care for them is they are a screamer. They make power at high rpm's. A beginner would be better served with one that does not operate that way. A lower rpm engine like the Super Tiger is a better choice. This is my opinion only. With some work and tinkering the TH engine can be made to run very well. I feel though you do not need this at the start.

Mark Shuman