This makes no sense at all.
I don’t know if I would trust a mechanic that had a bunch of high mileage VAG motors piled in the corner. That doesn’t make any sense.
It’s like if you went over to a ladies house during an amazing first date for a fun time. When you walk in you notice she has a pile of torsos in the corner of her living room. Why? Why would she not dispose of the bodies? I would seriously second guess a relationship with a woman that has hoarding tendencies.
This whole story is wonky.
Have your car towed to the nearest VW/Audi/Euro Independent Shop with an amazing rep in your area and get a second opinion.
The worst thing is that you’ll be out $100-$300 more for a tow and second opinion. Plus it opens up your options for building the motor if you decide to go down that route.