Clifford Development, working on a Williams FJ44-3A engine conversion for the Citation II, has appointed Chino, Calif.-based Threshold Aviation Group as a service center. Under the agreement, Threshold will sell, install and service the upgrade, which will include all necessary parts, certifications and manuals. Clifford is still developing the more than $2 million conversion. Downtime is expected to be six weeks. Clifford hopes to have the conversion available by the fourth quarter.