Although the original Essex engine has a reputation for providing a lot of torque it is a very heavy unit with poor power output for its size and hardly becoming of a sports car.
Replacing it with a modern lightweight engine producing twice the power with better fuel economy, cleaner emissions and better reliability is a much better idea.
I sourced my engine and matching 5-speed manual gearbox from a Jaguar S-type (the modern re-dressed Lincoln as opposed to the proper classic Jaguar S-type) and if you are looking to carry out this conversion I strongly suggest you do the same as you will save yourself a lot of headaches over trying to convert the transverse mounted X-type or Ford Mondeo variant.