Bob: The C85 is eligible for installation in the model C as long as the airframe has a trim tab, not a trim spring.
The most common props for this installation are the McCauley 1A90CF or 1B90CM. Length must be between 69.5" and 71" and any pitch that meets the static RPM requirements. 7148 - 7150 is considered "normal". All this information is spelled out in the type certificate. John Cooper, A&P Skyport Services PO Box 249 4996 Delaware Tnpk Rensselaerville, NY 12147 518 797-3064 Fax 518 797-3865 www.skyportservices.net
