Before I started (trying to get RC4.3 working ) with P3Dv2.5, I was a bit unsure it would work (since RC4.3 was never intended for P3D nor 64 bit operating systems). But in any case others are having the same doubt that I had, I have to say it was easy to get it up and running. Here below are the steps I did, that might help others. I will not mention it for each step, however WHENEVER possible choose right click an choose "run as administrator" in stead of simply running the programs and commands (that goes for starting CMD.exe as well):
Get the latest version of FSUIPC (by Peter Dowson), and install it with your P3Dv2.5 (and ensure it is working).
Download the lastes MakeRunways from Pete's site, put it into your P3Dv2.5 folder and run it (verify it generates the files it is supposted in generate)
Install RC4.3 and license it (get the key).
As per instructed on the pinned note "713 and unregistered dll's"Download "msstdfmt.dll" and copy it to your \windows\syswow64 folder
Start CMD (as Administrator) and navigate to the syswow64 folder, and execute the command egsvr32 msstdfmt.dll
Start RC (Configure as neede/prefered)
Generate your flight plans to FS200x format (PFPX can do this),
Load your flight plan into RC
Start P3D
Fly your favorite plane in P3Dv2.5, with guidance from RC4.3 :-)