If you have the entire car, then you're set.

Since this is 240D and you want a 300D I presume, the only thing missing from that particular car is the front section of DS and engine (and maybe shift linkages). I have the DS front section, and I can send you the precise measurements to make one. The DS front section will cost around $200 to get custom made. So, considering you have the entire package, swapping out the engine is EZ PEZY since the car is already set up to be a manual and a DS front section is likewise EZ PEZY.