I'm saying assumptions interfere with trouble shooting the cause.
All the questions come from the installation manual for a T56.
A T56 will not bolt up to a standard bellhousing. What adapter plate was used or how did the installer make the connection? A Quicktime bellhousing is one of the few that may not require runout adjustment.
If he's pointing the finger at the trans, ask him to qualify his work first. There's more defective mechanics than defective T56's.