The swap won't be easy. You're looking at essentially buying a new Laptop. The Inspiron 9400 supports Core 2 Duo and is the closest to your machine, but I think there are some physical differences in the construction, I've never had both machines side by side to get specifics but I don't think you're going to be fitting an E1705/9400 board in your current system. At least not without changing out several other components.
Laptops do not have a standardized architecture like Desktop PCs. There is no such thing as a chassis size number.