I have a stock 1967 Cutlass 330 with factory 2 bbl carb on a 2 dr HT. I am planning to replace it with a factory 4bbl carb and intake manifold from a 1967 330 Cutlass S.
Do I need to install a harmonic balancer along with the 4bbl?

 

No, that shouldn't be necessary.

 

The balancer is the same no matter what carb you got for 1967.