620TQ is probably an error on that guide.There are leaked GM engine docs that indicate that there are two 5.5L 32V engines, one NA and one turbo.
"LT6" NA 5.5L 32V at 600 HP 620 TQ
"LT7" Turbo 5.5L 32V at 850 HP 750 TQ
Making sense of the "Leaked" engine guide - CorvetteForum - Chevrolet Corvette Forum Discussion
What a disappointment this car will be with a pathetic 600hp motor. Getting its shit pushed in by 15 year old H/C c6z's. I will definitely be cancelling my order
Theres always one village idiot....Hopefully it's a TT V8 making good power , 600hp 3650lb C8Z will be on the pair what we had 15 years ago from 3100lb c6Z with 505hp