hey budda my dads got a running straight 8 in a 53 cheif 4 dr, they are a neat motor but i have been told their cranks can be a problem if you spin them too fast which i can see. i think anything you do may have to be homemade like multi carb manifolds etc. i would think any modifications that help a flathead 8 would help the buick like porting and bigger valves headers etc.
good luck if you are going to use the straight 8 . not a lot of them around hot rodded