If the bullet convergence point is offset from the center of the reticle like this, a change in the virtual pilot's position will not by itself help here. (Unless the reticle is incorrectly positioned close to the sight, instead of the proper, approximately 10m away from the pilot.) It would require to move the reticle via the cockpit hier.him.
Is this large offset the result of using this old mod? Those old meshes should not be used in much newer game versions, in case other changes to the mesh have been made during the intervening years.
If you have the latest IL2-Selector.exe, you can enable, via a check box, the dump mode. Check that box, run the game, fly a moment in the desired plane, then quit the game. (Remember to run the Selector, de-select the dump mode check box, and save.)
When you look in your game's main folder, you will see a folder named "dump". This will contain all game resources that were loaded, including, e.g., 3do/cockpit/J2M3, or something like that. If you have mods installed, those modded files will appear here. Therefore if you desire the stock files, disable any related mods.
Stock meshes will typically require to be converted to ASCII in order to be edited (the game will read the ASCII file format, therefore there are no concerns about having to convert again.) The easiest way to convert binary meshes to ASCII is via a handy little program called something like Mesh Viewer. With this program you navigate to a cockpit or plane or object folder and open the hier.him (or .sim file for objects). The cockpit or plane or object will be displayed, which you can manipulate for examination. There will be a menu option to save as text, which will convert all meshes currently displayed to ASCII. Now you can open the relevant mesh (such as Body.msh or MaineHull.msh) to change your pilot's viewpoint.
If you need further help, please ask. I can supply a link to the Mesh Viewer.
In the meantime, just what are you wanting to achieve in the J2M cockpit as regards the pilot's viewpoint? Is this for the stock cockpit, or a modded cockpit you wish to keep?