Sorry, and I don't mean to fbe flaming. But, 2 S&S B's is a bad idea... Too much venturi area for shovelhead ports. Snap the throttle open, manifold vacume drops to zero, no 'celerator pump to overcome the stumble, and a lot of time and money wasted. In the old days (Bobber?) some folks would weld up the heads on a panhead in order to run 2 left side carbs. It would eliminate the intake U-turn on stock heads. A stylish old carb to run that will perform is a Rivera SU! They have a huge tuning range and options for needles, springs and jets. Rivera will give good tuning support from their experience.
But if you must...I have a friend who has a twin carb manifold for a shovel. "Somebody" made it. It puts two smaller spigot mount carbs opposite each other with a plenum in the middle, one on each side of the bike. Might work with 34 or 36 MM Mikunis. But talk to the hot rod guys about plenum manifolds, they'll tell you they're only good for high RPM's. At 98 CID I think you're running 3 5/8 bore with 4 3/4 stroke. That stroke will limit you to 6000 RPM and if your manifold don't work till you're over 4500, it don't make a pleasant bike to ride.
Let us know how you make out.