If you have a friend in the legal profession, you need to take him along. Or, you can just file a "theft" claim with the police in your area. Either way will get the attention of the shop owner very quickly.
In any event, I would just discuss the situation with the shop OWNER (no one else will do on this one). Let him explain what he knows [he either doesn't know much about what happened....or he's the one who authorized the "procurement"] while you listen patiently.
If you "lose it" or blow up at the owner, it will do you no good--especially if you end up in court, later. You need to stay calm and make NO AGREEMENT, either verbal or in writing, unless he can assure getting you YOUR engine back. If he has decked the numbers of the block, there is NO WAY to verify that it is your engine AND YOU SHOULD NOT AGREE TO ACCEPTING AN ENGINE THAT YOU CANNOT VERIFY IS YOURS.
From my point of view, I would not accept any agreement for installation of any other engine, short of the shop installing a very nice, modern fuel-injected crate engine AND overdrive transmission of my choice COMPLETELY AT THEIR EXPENSE. If that doesn't work for them, take them to court and demand the moon and punative damages for lost value in your car.
I'm curious as to what people here think is the value lost due to the lack of a matching numbers block on a 1973 L48 coupe. My guess is $3000-5000.
While I would also be very upset, keep your expectations in check. I don't think bringing in lawyers (who aren't friends working for free) or law enforcement is going to help you get much more out of your loss.
If you can negotiate something in that value range, I would probably take it.
They don't misplace motors. If it truly is not there, they used it for someones order. If it is a numbers matching block for your car - that's a huge hit in the worth of the vehicle.
Since you're my area, please keep us posted on what happens and what shop this is. Oh, and don't let the chrome bumper guys fill you full of bs either. It may only make that much of a difference to them, but it doesn't to everyone.
Wow, I feel bad for you! Have to wonder how long the motor was there, I just can't see how they can misplace it. Is it a big shop and possibly it is sitting under or behind some other motor?
I know I'd be pissed if they decked my numbers matching L82 or lost it. That's why mine is sitting in the garage safe and sound with a crate motor in my 76. If I ever sell the car it will go with it and the new owner can do what they want. Until then it will sit there unless I decide to build it but for now I can build the crate motor how I want and beat on it all I want
Had this happened with Dover (cylinder head shop) Took them a head for a customer's car to be decked and valve job. 2 weeks later, still "not ready" then on the 3rd week they said they had no cylinder head for us, we never left them one. The finger pointing and arguing went back and forth for a while, but in the end WE had to buy the customer a brand new assembled head. They still deny recieving a head from us to this day.... and we will still never send them a $0.01 of business. This happened many years ago.