if I am not mistaken all of these products worked well with both of my Sims FSX and P3D4.3-4
Please clarify what's version your P3D4 really is, since P3D4.3-4 is not very clear. If it's 4.4, it should work without any issues, since 4.4 is the minimum supported version under P3D4.
If it's 4.3, then no, there's no chance it will ever work, since last year we made a huge update, like a complete makeover of almost all GSX vehicles/objects, to be remodeled with better quality and textures, and they are almost all PBR now, and since we use many specific functions of the P3D4.4 SDK that are simply not available in previous version, like the Render to Texture API, the Camera API, the Mouse API, and others too, there's simply no way for us to support anything less than P3D 4.4, although everything will work so much better with the latest version, which is 4.5 Hotfix 2, that fixed lots of bugs and improved color rendering quite a bit.
Of course, the current GSX 64 Bit installer will check the version, and it will tell you it cannot install into any older version.
Instead, the 32 bit version, can only be installed into FSX, FSX:SE, P3D 2.5 or P3D 3.4, you can't install the 32 bit version in P3D4.
If you have both FSX and P3D 4 ( 4.4 minimum ), just download and install both versions. They use a shared folder, outside the sim, so no unnecessary duplication of files will happen, and they are designed to work that way.