The actual conversion\porting over for Most HJG aircraft from FS9 to FSX is fairly strait forward. Good direction is provided within the installation instructions for each aircraft and panels.Most textures are also compatible for both versions.
Basically the only changes required are for the Aircraft cfg. For FSX just delete the fs9.cfg and rename the FSX.cfg to Aircraft.cfg and then add your textures. The same applies for the Panel for some but not all require this.
Also delete the Sound folder and download the required Sound from the HJG download page.
The only hitch is the panels on some of HJG's aircraft are not compatible with FSX. So sometimes I've used the HJG panel background and updated the gauges to fsx gauges preferably the correct ones, not just some default. Sometimes the Radio section in Aircraft cfg. needs changing so the vors will operate. good luck. There are less problems with HJG's then some other fs9 models from somewhere else. Turbo props sometimes need a tweaking air file.
PLEASE NOTE: The term "FSX COMPATIBLE" can be misleading or misinterpreted by some .... given there's such things as FSX nativity as well as FSX compatibility/portability.
When HJG states a files is FSX compatible .... it's simply saying such files are "FSX PORTABLE" .... and with no known issues of any significance that can detract from the enjoyment of these files.
If there's the slightest degree of incompatibility of any of our files with regard to FSX .... or .... if we're not cleared to market any file as FSX compatible/portable by those who's files we host to by consent, then, such files are marketed by us as being "not FSX compatible .... despite any evidence of their successful FSX portability.