[Forager]

In your MODS folder create a folder. Name it for example "Freddie P51". Then open it and create a folder named "3do". Open the "3do" folder and create a folder called "cockpit". Open the "cockpit" folder and drag&drop the "P-51D-20(K14)" folder from the rar file into it. It should be like this at the end:

C:/Progs/Il-21946/MODS/Freddie P51/3do/cockpit/P-51D-20(K14)

Hope this helps people who aren't really familiar with the order of folders.

Mr.Fox, the above procedure fixed the problem for me, hope it works for you.