The Bav motor is a 2.8L M30, so the manifolds will fit, though the ports may be smaller than your head intake ports if you have a 3.5L.
Are you looking at the stock 35/40 INATs (Zenith/Solex) or replacement 32/36 DGAVs? I ask, because if you're planning on installing them on a 3.5L M30, the INATs may not provide enough CFM (you'll have to do the math to find out) -- and since DGAVs don't really provide enough CFM to a 2.8L at WOT, they'd be pretty hopeless on a 3.5L.
FWIW, the 630CS used a single, downdraft intake with a 4-barrel Holley parked on top. That car was never imported into the states by BMW, but for some reason, there's a bunch of them around -- mostly rusted up, so given the range of Holley (and their ilk) choices available these days, that might be another route to pursue. Be sure you grab the linkage as well as the intake manifold if you do.