Nick-
That is a Briar McKay Manifold with 4 Weber carbs. Briar MacKay worked with Traco Engines and Bill Thomas Race Cars were trying this setup on our engine dyno when Terry was at the shop. I did remember him asking about it but the car left Long Beach with a 4 barrel Holley and Weiand manifold. It was available in aluminum or magnesium. MacKay also made water pumps for the bi block in Magnesium. Interesting placement of the brake booster...............

Ron Ogilvie