Making them: you can buy the harpy wings from
GW site under the bitz section.
use a standard gaunt bost (hormagaunt one) with fleshborer arms.
add the harpy wings and its done, simple and effective (and cheap)
Using them: they should be no problems to use atall, aslong as they are on the right bases no one should moan.
they will actually look better aswell

(
GW ones look cheap and tacky)