Over $6000 to install TTI headers on 66 Barracuda

If he refuses to give the car back before payment is made, call the cops in!

Cops probably won't get involved. They usually don't in a civil matter. The Mechanic has every right to hold your car until payment is presented. What you need is a Judge to order the release of the car. As in "Court Order". The BAR should help in this area. They have ways of getting Mechanics to release cars.