I have been told by 2 clock repair shops that the movement (340-020) in my 74 Hamilton mantel clock is unrepairable...is a replacement movement available and at what cost?

John Williams, January 2013

Just check on the web for clock parts as there are several suppliers that you can get movements from; try R&M Imports. Remove the hands, remove the wood screws that hold the movement to the front of the case (accessible from the back) and pull the movement out. Revers the process for putting the new movement in.
By the way, there are no "unrepairable mechanical movements" but they can be more expensive to repair than replace.

Stevens Clocks, February 2013