383 rebuild - kinda whimpy on the dyno?

but then my instinct of “hey, you’re the expert here” took over and I let him run the show. If there is a next time, I won’t be so passive.
That's fine. There's always something to learn and IMO it always is better to be respectful of a person's experience. If you go back, you can then say 'hey, I'd like to run it a bit higher this time.'