Any reputable transmission shop should be able to do the job. Buy the PTU off tasca along with a compression seal, a half shaft seal kit, and about 2 or 3 quarts of mercon lv. Should run you about $800 all together. Labor should run about $500 for the job.
If you're set on Ford installing it, buy the parts yourself and see what they'll charge you to install. Dealers like to rip you off on part costs.