Hi There celestial being
I would highly recommend teh Hitec HS65HB servos for use in most non 3d 450 helis.
http://www.rcsmart.com.my/webshaper/store/viewProd.asp?pkProductItem=540But Anwar is correct most 9 gram servos will work well.
If you want a very high quality servo you cant get much better than the
Hitec HS 5065MG they are fast smooth and strong with very good centering.
http://www.rcsmart.com.my/webshaper/store/viewProd.asp?pkProductItem=2226I believe Hobbyland here in DOha have these servos for QR170
Another high spec servo in that size range with better specs and a cheaper price than the HS5065MG is the MKS / Turnigy DS530
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idproduct=9657If the servos you are looking for are just for the retracts then the HS65HB will work well.
Hope this helps