Mike,
The power Torque (Contractor) sounds like you will have to rebore the cylinder & replace the piston,rings,bearings and gaskets. That is a major overhaul.
The 160 sounds like just a piston ring replacement which is not that hard to do. You can purchase workshop manuals on ebay for about $15-00 which would help you a lot.
The quoted price from the mower shop sounds correct as the rebuild takes a lot to do and usuall takes up to a day to do and as you know wages are not cheap these day.
Regards,
Bruce