Manifold question

Who knows what about an offenhauser "360"?
I have one I was thinking of putting onto a 318 powered B body when I put my 302 heads onto it, my other choice on the shelf is a regular (non air gap) performer. The 360 looks like a single plane with a center divider.
Don't single plane manifolds draw less vacuum than a dual plane intake, with all else equal?
Though I THINK I remember back in the late 60s the 318s ran a single plane 2 bbl. Though it's been a while since I have worked on one, since my brother had his 68 charger.
I am doing a lean burn ectomy and since the original carb needs rebuild anyway, I have 2 choices of carb at my disposal/ actually a couple of each: a 500 and a 600 AFB, as well as a couple of TQs. Which manifold would you run on a cruiser that occasionally is used like a daily driver in warm months? I'm also considering a small cam, a comp 260 among the bigger of the 2.