Bought a set of Gil manifolds - no turbulators. Are they needed? i have the newer style HP500 arched risers.

If it's a stock Mag cam it should be fine. Merc put them in there from the factory on Late HP 500s for a reason. If anything it helps with condensation.

its a customer roller near hp500 specs but little tighter for better idle/low speed usage

If it was me I would get them, Hardin (CP) has them as well as the gaskets a lot cheaper than Merc prices.
I have them and silent choice too with no issues (knock on wood) in an HP500 with late style tall risers.

pm me your phone number i will give them to you
going out to the shop to dig em out right now