That is true, I did very little work to the manifolds. I opened up a couple of ports that were smaller than the gasket and that was it. The manifolds I used did not have flapper valves. The big "trick" on my setup was the custom flanges I had built to go direct from the manifold to a 3 inch pipe. I had thick flanges machined from SST with an internal step so the 3 inch tube would slip in place.

I'm still running the same setup today although I have a different engine. I sold the 470 low deck a long time ago and replaced it with a 512 inch low deck. The 512 makes a little more power but is still very mild. I think the cam in the 512 is 240 @ 050, might even be a bit smaller than that. Has plenty of vacuum at idle and lots of torque down low. It has been a long time since I worked on the car but I think it made around 500 rwhp which puts it right up near the top of any musclecar list.