273 or 318 or both help

273 and 318 are both internally balanced so that shouldn't be an issue. Only issue is what was already brought up, about timing mark location related to the timing cover that is used.
Given the age of the damper I'd send the damper out to either damper doctor or damper dudes and have it rebuilt.

My question is, what became of the 87 d150?
Being from Arkansas it's probably not as rotten as one that's been around here. What was so bad about it that you decided to pirate the engine to (potentially) put in the cuda?