Most of the issues in these engines originate in the head, the bottom ends are pretty tough. If you're getting a used engine, you may very well have the same problems yours already has, or require similar work as you'd already be doing to the one you currently have. Shelling out money for a used engine with a #14 head (which is likely what you'd be able to find for cheap) is just throwing good money after bad, not to mention the challenges of actually doing the engine swap itself!