Where to start?

oldfish,

as a 65 formula s owner I would say leave that beauty alone! It is too nice a survivor to mess with. Mine was mechanically restored but since we did not have the original 273 I put in a 318, but uses manifolds valve covers from 273 runs and looks good. Yours is so very nice as it is, the most I would consider is finding a 273 4bbl manifold set up and keep original looking. JMO One must do what makes them happy..