I think you took the toughest possible line here. V's ridiculous 3 bet sizing is very polarizing but combined with his tiny remaining stack, Hero's loose image, and our hand strength I think I'd rather just 4 bet pre since we are OOP. Flatting is also fine but I really don't understand donk leading $75 on an Ace high flop when V only has $150 left on the flop. We can never fold to the jam so we lose the max and will win the minimum unless V turns his hand into a bluff which you haven't indicated the tight player had a propensity to do. This should allow V to fold most of his bluffs and play perfectly. When he comes over the top with no fold
equity he should pretty much always have Ax. If we are far enough out of line that he still thinks 99 is good then he's going to bet if we check anyways and we can bluff catch a much wider range (KQs, KJs, and all those middling pairs). When we donk lead some of those combos will give up and he should only be continuing with the top of his range. I've seen middle pairs like JJ and TT make these huge raises pre trying to buy the pot and avoid a flop. It could be a sizing tell to look out for. KK+ would more likely want action from the lose UTG open. Congrats on taking it down though.
Also, effective stack is a term used to indicate the smaller of the two players stacks. It's confusing to refer to Hero as having $850 effective since you've already said V was playing $250. The math is still a bit confusing. It sounds to me now like V had $350 effective pre flop? Which means if we donk lead $75 and got jammed on we would need to call $175 to win 532 (-rake), making the total pot 707. If he had $250 left on the flop I dislike the donk lead even more. If V was $250 effective then we would have to call $75 to win 432 (-rake), making the total pot 507.