Ian,
The vertical drag estimate is a rough one, based on the fact that the wing is a flat surface presented to the rotor downwash, thus creating some vertical load. For a normal helicopter, the fuselage usually creates about 4 to 5% download. For a tilt rotor, where the wing is large, and the downwash velocity is high, it is up to 12 to 15%. The H-56 had a wing sized somewhere smaller than a tilt rotor but much more than a simple fuselage, so I guessed 10%. That means the wing costs about 1000 lbs of payload relative to a helicopter.
The fan in fin Blackhawk flew in 1974, and the Fantail S-76 flew in 1991. We did study the old data to help lay the S-76 out, and it came in handy, especially the duct shaping, which is critical to the efficiency of the fan.