If you have to ask that question, then you should probably dump it. I have always thought that it was better to fix what you have instead of replacing it with someone else's problem, which is what already happened to you. If you fix what you have, then you KNOW what you have. If you spend $450 on a top end and $450 on a crank, then you have a solid engine that you know will live. If you dump it and buy another one , you are gambling on getting something decent. How many time do you want to do that? If you are going to replace it make sure you check out the next one thouroughly- check compression, condition of fluids and levels, proper test ride, look for broken, bent or missing parts, etc.