Along with what kip Foss and New2MBZ have stated, you might want to set up an account (just on paper) -- put down owe "1st shop" $x for chain and rail --- and then subtract from that the costs of any repairs that are needed (to bring your car back to nominal) as a result of damage done by the 1st shop -- if they still have a positive balance give them that with an explanation of how it was calculated -- write on the back of the check, above where the endorsement will be made: "payment in full" and "this check is an accord and satisfaction of all debts owed" (make a copy of the front and back of the check for your records).
This way you will feel better about getting any value from the 1st shop, you will cover the damage done and you will have a defense against a mechanic's lien should the 1st shop have second thoughts about returning your check.
best of luck
1986 560SL (52.5k miles) sold 11/24/04
1987 560sl (55.6k miles)