See
http://www.tocmp.com/brochures/Buick/1936/index.htm http://www.buickclub.org/ The first step is to determine, from the casting numbers and serial numbers, exactly which engine you have. Buick made several versions of the inline eight, depending on whether it was intended for a Special, Super, Century, Roadmaster, or Limited. The big one is 320 cid.
Your quickest route to a shop manual and specifications for your engine is probably a Chilton or Motor manual in your local public library. These manuals are usually available in automotive swap meets and are fairly inexpensive. You can also find original shop manuals and parts books for sale by literature vendors, but they will be more expensive.
For Buick parts, see
http://www.oldbuickparts.com/nos/36parts.htm Buick parts and literature vendors also advertise in *Hemmings Motor News*, and you can find many of those ads online.
In the early 1940s Buick sold a factory dual manifold for these engines. You can also find factory and aftermarket single-four-barrel manifolds from the 1950s, but they are, i believe, more rare.
God's Peace to you.
d
Inliner #1450