Bolting back together the parts that are mismatched and failing WILL fail again.
Do you really believe this shop you took it to has any idea what they are talking about? 99% chance no one in that shop has ever done any work on or have any experience with inline sixes.
or did they just tell you what you want to hear?
It's still wrong. Having driven it 8k like that is in no way any type of longevity.
Adapter plate is still the wrong answer, and if they were willing to make an adapter, that's isn't going to be covered by that $921 dollars you just threw away. Add a couple thousand to that.
Keep looking for a motor.
$921 for what? To again bolt together the wrong parts? The way to make it right is to actually get the correct and compatible parts.
That motor certainly wasn't $921, you could have put it together yourself and been driving for a few weeks by now.
Ask that shop about the bell housing see-sawing up and down across the only 2 bolts that are thru the bell and into the block. The spacer plate is in no way strong enough to hold the bell and trans rigid to the block.
It's wrong, doesn't work, and still isn't going to work for any amount of time.
Honestly, do you think they did anything other than bolt it together the exact same way you have 8-10 times?
Are you now going to blame this shop for it not working, knowing it is parts that don't go together? Even after multiple people have given you advice and information about transmissions, clutches, and blocks.
1000% sure the collective knowledge and experience of the people on this forum far surpasses that shop.
Again you are posting the exact same issues.
The answer to every issue, noise, grind, bang, clang, tick, and shudder coming out of your setup is YOU CAN'T PUT A 9" CLUTCH ON A 8-1/2" BLOCK..............................