Is there an RD4 for FSX yet?
I would suggest that you keep an eye on Middle Atlantic Air Museum because they have excellent software including the R4D. If you hold your breath, I am sure that Bill Rambow and his group will have an update for FSX.
PS: I took this picture while attending their WWII show in June.
Is the DC-3 insufficient?
MAAM FSX update.
http://www.maam.org/flightsim/enhance/r4d_enhance.htm#FSX BASIC COMPATIBILITY UPDATE FOR R4D/DC-3/C-47 CD